External drive question about erasing doents off the drive? HP SimpleSave.. Any "computer wizes" out there?

I'm using an HP SimpleSave external drive to transfer information from my desktop (running in safemode because it recently crashed) to my new Macbook, however when I put doents onto the drive, I cannot erase them from the drive folder after I have saved the ones I want onto my laptop. This is a problem because I am only doing about 30 doents at a time to sort them, seeing which ones I would like to save/erase etc.. Please help a confused, rather computer illiterate person! =/