I think you may be referring to Hard drive space.
Empty your trash in the dock
If you use iPhoto, open it, and select the "trash" in the left column, and empty that too
Check your download folder, as you may have data in there as well
Thank you, i bought WhatSize app. that was suggested on that site and i set 20 gb free.
If anyone has a similar problem just buy WhatSize app in App Store, and you will not regret.
It shows you all files stored on your mac and helps you see where last kb went.
To all of you that have more memory taken up in "other" check your user->library->messages->attachments folder. It basically keeps all the files you've ever sent to others in imessage. Mine added up to 35g, so quite happy when I could delete all that useless stuff!