The below process shows how to migrate an OCS 2007 R2 user to Lync 2010. This cannot be done using any GUI driven tools (at time of writing)
Note: Lync users cannot use the Microsoft Office Communicator 2007 client to log into Lync 2010. If the user to be migrated is logged in and using the Communicator client they will be automatically logged out and an error message informing the user to upgrade their client.
1. Launch the Lync Server Management Shell from your Lync Server
2. Type command: Move-CsLegacyUser -Identity username
3. Confirm the user move.
4. You're done.
Install the Lync 2010 client and enjoy. :)