You may use the CS-RCS Change Explorer to undo any change. You can also retrieve any valid revision to the work folder and check it in to make it the current head revision.
Since deleting revisions is error-prone (for instance, you are not able to re-build a project milestone containing a deleted revision), deleting arbitrary revisions is not supported from the CS-RCS GUI.
Note: RCS uses an efficient reverse-delta algorithm and only keeps the delta between revisions