Changing a user's Sales licence tier

What it does

Moving users between Sales Professional, Sales Enterprise, Sales Premium and Microsoft Relationship Sales is a four-step operation: buy the new subscription, replace the licence on each user, install the app that goes with the new licence, and remove the solution belonging to the old one. Microsoft documents the same process for every direction of travel.

Key facts

The upgrade process is identical regardless of which licence you are moving to. There is no tier-specific migration tooling.
Step one is buying the subscription in the Microsoft 365 admin center under Billing > Purchase services.
Step two is per user: Users > Active users, select the users, then Manage product licenses > Replace and pick the new licence. Replace, not add — leaving both assigned is a common source of confusion later.
Step three is installing the app that matches the new licence, from the Power Platform admin center under Environments > Dynamics 365 apps. Sales Hub for Enterprise and above, Sales Professional app for Professional.
Step four is deleting the previous solution from the environment (Settings > Advanced Settings > Customization > Solutions). Microsoft's own warning: deleting the solution removes the associated app modules and configuration such as site maps and form preferences.
The Licensing Guide, not Learn, is the reference for which app corresponds to which licence.
Data is retained when you switch licences. Sales Insights data is only deleted after 30 days if the licence expires, and then only if no other related licence exists on the tenant.
You need admin rights in two places: licence management in Microsoft 365, and environment and app management in the Power Platform admin center. In most enterprises those are two different people.
Moving down a tier is not separately documented. Learn describes upgrades; the downgrade path has to be reasoned about from the entitlement side, and the app and solution swap works the same way.
Mixed-tier environments are supported. You are not obliged to move everyone at once, which makes a phased migration viable.

When to use / skip

The upgrade path from Professional to Enterprise comes up on real projects more than anyone plans for. A client buys Professional on cost grounds, hits the entitlement ceiling somewhere around the first serious automation or integration requirement, and then wants to move without rebuilding. The good news is that the data stays put. The bad news is that the app modules, site map and form preferences that live in the outgoing solution do not, so the "upgrade" is closer to a re-implementation of the presentation layer than a switch being flipped.

Enterprise to Premium is much less disruptive in practice — you are turning on capacity and features on the same Sales Hub app rather than swapping apps — but treat Microsoft's generic four-step process as written and check what the solution removal step actually removes in your environment before running it.

Skip the whole exercise if the client is only trialling. Trial to paid is a different flow and does not need a solution swap.

Configuration decisions

Whether you move everyone at once or in cohorts. Cohorts mean a period of mixed-tier running, which needs the UI to behave sensibly for both groups.
What you do about the customisations sitting in the outgoing solution — extract them into your own unmanaged or managed solution before the removal step, or accept rebuilding them.
Whether the new app gets a fresh site map and form set, or whether you replicate the old one. On a Professional-to-Enterprise move this is the biggest scope item.
Who runs which step. Licence replacement and app installation are usually different admins, and the sequencing matters.
Whether you rehearse the move in a copy of production first. For Professional to Enterprise, you should.
What happens to security roles. The new app has its own access role (Sales Hub uses Sales, Enterprise app access), and role assignment does not carry across from the old app.

Gotchas

Deleting the old solution removes app modules, site maps and form preferences. If your client's carefully tuned forms live in that solution, they go with it. Export first.
Replacing the licence in Microsoft 365 does not change what the user sees in the environment until the right app is installed and the right role assigned. Expect a window where users have a new licence and no working app.
A user left with both the old and new licence assigned will not error, but you are paying twice and the app visibility becomes unpredictable. Use Replace.
Sales Professional environments are told to hide the Sales Hub app if it appears. After an upgrade you need to reverse that, and people forget the app was deactivated rather than absent.
Sales Insights data survives a licence switch but not a licence expiry — 30 days after expiry it goes, unless another related licence covers it. Lapsing a subscription during a commercial renegotiation is a real way to lose it.
There is no rollback. Once the old solution is deleted, going back means reinstalling and rebuilding the configuration it carried.

Consultant notes

Tell the client plainly that a Professional-to-Enterprise move is a project, not an admin task. The data survives; the app experience does not come across for free.
Take a full solution export and a screenshot pass of the site map and key forms before anyone deletes anything. It is ten minutes that saves a week.
Do the move in a sandbox restored from production first, and time it. That number is what the client actually wants to know.
Check the licence-to-app mapping in the current Licensing Guide rather than from memory — it has changed shape more than once.
Before go-live on the new tier, verify every migrated user against three things: licence assigned, app installed and visible, role granting app access.

Worth another look if Microsoft ever publishes a proper downgrade path, or changes the solution-removal step.