If your recovery drive is full, the only way to free it up is to remove the files that shouldn't be in there. This requires a more detailed answer in order to convey what the issue is, so I'll explain what's likely happening below.
Depending on how well versed you are with computers, you likely don't think about the recovery drive too much. Under normal circumstances, you will save and store and personal files on the C drive.
The recovery drive, or D drive, houses pre-installed recovery files that are activated when you enter the restore disk usually provided with the computer. Personal files should not be stored on the recovery drive, but something this does occur, and it quickly becomes full.
How to free up the recovery drive?
This is a little tricky, and it really does depend what files are causing the recovery drive to become full. If you can see obvious personal files within the drive then you can remove them to see if that correct the issue.
You should be very careful not to remove any of the recovery files, so if you're not sure what you're doing, you're probably better off seeking the advice of a professional. If this problem reoccurs then you should definitely take your computer to be looked at by a specialist as the recovery drive should not be housing any personal files.