unable to free up space on samsung s3 mini

I've got a Samsung S3 mini. It keeps telling me that I have insufficient space. I have just deleted loads of photos and videos, I only have a few apps. Instagram, pinterest, watsapp and picsart. I deleted two of the apps but it's still saying insufficiant space. I have no idea what i'm doing wrong? I have restarted the phone to see if that helps but NOTHING. When I've gone into storage it says that I have 810mb in the downloads...so i clicked on it and cleared the two things that I had in there, it's cleared them but is still saying 810mb.. HELP