Well...I'm not sure, off the top of my head, how to delete individual recovery files, but I can tell you something that might be equally useful.
Go to the Control Panel and double-click System (Or press the Windows Button between the CTRL and ALT keys, plus the Pause/Break button). Click the System Restore tab. Click the Settings button. Now you can move the slider to tell Windows how much hard drive space it is allowed to use with System Restore files. It works on a first in, first out basis, so if you just decrease the amount of size available to System Restore it should automatically ditch the oldest files.