you'll need a ratchet or t bar and some have a torx bolt some are a caphead bolt (hex key) and theres 2 of them on the underside of the bumper.I think 10 or 12 mm alen key or torx equivelant type sockets with the male bit in them,not the female type socket.
Or you can take the mounts off with a 13mm (i think) spanner,3 each side or is it 2,been a while, but are normally rusted to shit.
I've removed the front and rear bumpers on two E30's, '88 &'89, and all the bolts came undone fine. You just need a long breaker bar to make life easier, and copper grease them when you put it back togeather.