I was using Win7 on an HD with all the programs like Excel. Recently, I installed Win 8.1 on a new SSD and disconnected the HD with Win7 on it. Can I, and if yes, how do I uninstall Win7 from the HD without affecting other program on the disk which I would like to use with Win8.1?
As bassfisher says you can only move user data files to another system. When you install programs the install process make registry entries and many other system changes which are "tied" to the operating system under which you installed them. If you want those programs to run under Windows 8.1 then they must be re-installed under Windows 8.1.