It's not that difficult, I haven't done this to a honda head, but to lotus europa motor,
the head is aluminum and the guides are usually brass, they have different co-efficients of expansion. you need to hea the head up to some temperature (I think about 100-150deg C) , I can't remember what I set it at before but it needs to be below the value at which heat treating is done our you'll warp and ruin the head. after the head it heated up you can push the brass guiges out, push from the bottom of the head (the bottom is where the combustion chamber meets and you can see the valves) they should slide right out, and you'll need to heat the head again, to push the new guides in.