Deleting Old Backup Drive

I had E: as my backup drive.  Then I added a new drive F: and my backups now go to that drive.  However, Ghost has both E: and F: listed as "backup drives" and gives me errors because there isn't anything backed up to E.  How do I convince Ghost that E: is no longer a backup drive?  (No option to make any changes in "Manage Backup Drives" because there isn't any backup data on E:.  In fact, E: now has "live" data and is part of the backup job to F:)