Now that you have become familiar with how to use the helpful Upgrade Advisor, you’re ready to begin your extensive pre-upgrade testing phase. After you resolve all the issues you can, it’s time to take the next step: install SQL Server 2012 (in your test and development environments first, of course).
Three different paths lead from SQL Server 2005, SQL Server 2008, or SQL Server 2008 R2 to SQL Server 2012:
You can upgrade your existing SQL Server 2005 SP4 or later, SQL Server 2008 SP2 or later, and SQL Server 2008 R2 SP1 instances in-place, using the SQL Server Installer.
You can install SQL Server 2012 side by ...