Upgrading SQL Server 2008R2 to SQL Server 2012 in 5 minutes
Link to downloadables i.e. SSMS 2012 and Express databases
https://www.microsoft.com/en-us/downl...
Official list if potential issues during an upgrade
http://technet.microsoft.com/en-us/li...
http://msdn.microsoft.com/en-us/libra...
You may also want to check the discontinued features page:
http://technet.microsoft.com/en-us/li...
Run the Upgrade Advisor before you upgrade
http://technet.microsoft.com/en-us/li...