Macbok Pro Retina Memory Full - Help Me Wipe

I have a 128gb MacBook Pro retina bought in 2013. It is a work laptop so I do not store anything on it e.g. music, videos, photos yet the memory seems to be filling up. Only got 12GB left.

With the support of Apple I erased the disk, but that has not seemed to help. It is easy for me to reinstall the key programs and files from dropbox. Is there a way to fully wipe the disk just leaving the OSX then import files from dropbox?

Thanks,
Rich