File management

I know there is a SOLVED entry for this but it doesn't solve my issue.

I have 2 HDDs one for software the other contains all the data--"My documents" and all my email is on the D Drive along with other stuff that I don't need/want backed up.  So My documents is backed up as a file and folder backup.

All is fine except that I need a way to limit the size of these backups since the amount of backup is too large.

So how do I delete old file backups without losing data?