Small jeweler's phillips head screwdriver and a T6 Torx driver. Check out the procedure at ifixit.com. Not a big deal, just go slowly and don't start yanking on the top cover, especially the front edge of it.
LOL funny you should ask, I seen some really hokey stuff the company had a 9.5mm and it was taped in, not worth it until they make it 2.5" I don't want my HD floundering around in my mac. Oh that was a MBP.
Come to think of it i think the drive i a talking about is a 12mm cause its a 3 platter