After upgrading TFS, you should do a quick smoke test to ensure TFS is running as expected.
Figure: New TFS Title using our existing url
Navigate to the web access URL for your new TFS server.
If it loads correctly, click "Browse all..." to check all your Team Projects were migrated across correctly
In Visual Studio, connect to TFS, then:
Do a Get Latest on a project or file
Make a change, and ensure you can Check In