If you are talking about 2 partitions on a drive...
Right click on file(s) that you want to move. Select Cut(CTRL+X). Right click in 2nd drive space right click and select PASTE (CTRL+V). If worried go copy, then paste. Delete the old copy when you are sure files are moved and usable
Another way is to have 2 windows open side by side, one for eash drive partition. Drag files from old window to new window.
this only really works for data files. For programs you will have to reinstall so the Windows register values are correct.
edited for fat fingers