I think you mean the hexagonally-screws to get off the CPU with the cooling fins. For those you will need an allen wrench with 2.5mm. To get at the two screws in the round hole of the middle from the cooling fins you will need an extra long allen wrench (minimum 16cm or longer).
The other screws at the CPU brackets are called torx screws (looks like nearly a star or something like that)
Hope it will help you.