Total of four 6mm allen bolts hold the pump. Three of them are very easy to remove. However, the bottom front one can't even be seen. I recommend looking at the new pump so you can get an idea of where it's at.
The best thing to use is a long swivel (round head) type allen key (socket type is too thick). Go in with the long end and place some kind of extension on the short end, so you can break it loose.