If you already have an older fully set Ghost, then just select the newest current full MAME set, which as DC said is the [FREE] MAME 0.122 one, and when you open it in uTorrent, or any other torrent client you are using, then point the location you wish to save the files in at your current older set. The torrent client will compare your current files against those in the new torrent and work out what it needs to download to update your existing MAME set to the current one. Therefore you will only download the differences, which in this latest set is only about 200MB.