Could you give us a little information on your machine. since it has mint 8 on it I'm assuming it's quite old.
what processor? how much Ram? is it 3d capable? (if not you'll have to go with mate or xfce)
I would say you should go with mint 13.
you can install mint 13 over mint 8 by selecting the other tab when presented the partitioning page by the installer.
the select the mint partition and tell it to mount it as / and format as ext4.
Hope this is helpful.