you dont need a tool.
there is a small allen bolt on a lock ring undo that and take it of. (screw off)
tap the axle where you took the ring of and it will pop out,
take there driver out (bit with your cog on it)
then if you lok on the inside there is a small plate nearest to you, get summet in there and crack it a couple of times evenly around and it will pop the bearing out(take note of what comes out in order). then you can fully service it cleaning everything and oiling it up again the just push it all back in and tap the bearing back in with a soft hammer.
reverse the process and shabang!!
could be a bit risky if your new to it but meh works for me.