iFixit

You can skip this step if you bought your putty knife from iFixit. Putty knives purchased from iFixit come with pre-ground edges.

You'll need a putty knife in order to open the case. A 1.5 inch thin putty knife will work well, but you'll want to grind the edge down. Rub the putty knife's short edge back and forth on a sheet of all purpose rough grit sandpaper (100 grit will work fine) until it attains a beveled edge.