Second hard drive working. What can be deleted?

loop_it1

Honorable
Sep 17, 2013
5
0
10,510
A while back I installed an old hard drive into the second hard drive port. I finally recognized it and now I want to get rid of all the old windows and program files and basically make it extra storage. What can I delete from the old drive and still make it usable by windows 8? I am already moving the user files to the pre-installed hard drive. After that's done can I just format the old drive?