For some reason, the option 'Install Upgrade Advisor" on "SQL Server Installation Center" is dimmed or not available, even with all of the perquisites are met.
Solution:
Download it and manually install it.
http://www.microsoft.com/en-us/download/details.aspx?id=29065
Expand "Install Instruction" on the page - the Upgrade Advisor is close to the bottom, download it and install it.
Please note that after installation, there will be a separate menu under the Microsoft SQL Server 2012 folder for the SQL Server 2012 Upgrade Advisor. The "Install Upgrade Advisor" on Microsoft SQL Server 2012| Configuration Tools | SQL Server Installation Center or (x64) | Planning | Install Upgrade Advisor is still not disabled.
