"Unshelve pending changes" used to appear underneath File --> Source Control menu in VS 2010 but you won't find it in the same place in Visual Studio 2012...
Instead Unshelve has been moved inside "Pending Changes" within "Team Explorer"
Here is how to Unshelve pending changes in Visual Studio 2012
1 – Open ‘Team Explorer’
2 – Click on ‘Pending Changes’
3 – Click on ‘Actions’
4 – Choose ‘Find Shelvesets’
5 – Enter the user created Shelveset
6 – Find the Shelveset from the list, right click and ‘Unshelve’
