Proper way to upgrade from SQL Server 2008 R2 Express with Advanced Services to SQL Server 2012 Express with Advanced Services?

Hi everyone,
  Now that SQL Server 2012 is out, I must admit I'm questionning myself about:
What will I gain by upgrading from SQL Server 2008 R2 to SQL Server 2012? What is the proper way to upgrade to SQL Server 2012?               1- Uninstall 2008R2 and then install 2012?
              2- Use the upgrade section of 2012 setup program?
I'm actually studying Reporting Services.  The books I'm using are targetting SQL Server 2008.  Is there any major differences in 2012 so I might expect having problems going on with my readings? I would really like to have your comments/advices on these.
Thanks in advance for your help!

Stéphane
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