hmmmm...
delete them? that might do the trick
Seriously though, just use a root file explorer and you can delete any files you want. I recommend solid explorer. Another way to easily clean up your sd card of junk is to get airdroid and then you can hook up to your PC and manage your files that way. Though, Airdroid does not allow you to explore root on your phones internal drive, it just allows you to view your SD card files.
All the backups you've made using CWM are located in cwm/backups on your SD card. I would definitely only keep one current backup because they are quite large files.