Is there any simple solution to move collections form TFS 2010 to TFS 2012 Including source code, work items, documents, project site... ? by the way, TFS 2012 has been installed already.
I would need to import the TFS 2010 database(s) into TFS 2012,that already have people using the TFS 2012 environment. The Rangers Guidance can help I with migrations
Another option is to use the collection detach and attach operations. These support upgrading the collection at attach time. Even though this link says 2010, it will work with 2012 as well.
http://msdn.microsoft.com/en-us/library/dd936138(v=vs.100).aspx