Upgrading a multi-server SharePoint farm from Standard to Enterprise

1. Stop the Timer Service on all machines in the farm except for 1, in my case I left it running on the APP server.
2. Add the new product key and hit OK to start the SKU upgrade process in the Central Admin GUI.
3. Watch the event log of the APP server and wait for an entry with a source of “SharePoint 2010 Products Configuration Wizard” which will inform you that it was Successful.
4. Start the Timer Service on the next machine in the farm.
5. Watch the event log and wait again for the successful entry…
6. Continue with steps 4-5 on all additional servers in the farm.
7. Once you’ve received all successful entries in your event logs, a minute or so later you should get a successful notification in the GUI for the SKU upgrade.