Head has to be removed. Starting with removing timing belt, camshaft holders, camshafts, then loosen the head bolts by the sequence. remove head, place it on a bench get a valve spring compressor from honda, compress the spring, remove the retainer holder, then retainer, then slowly release the spring, remove that, then valves should fall thur. Then take it to a machine shop to have the seats, and valve margins resurfaced, and head cleaned, and dont forget to buy new valve seals. Then reassembly is reverse of the removal prodcedure. You would be better off getting a Prelude service manual. so then you have the specs for loosening the bolts, and torquing the bolts, etc..
My rebuild cost me 125 bucks, that included grinding the seats, valves, and steam clean the head, head resurfaced, by the thickness of a paper.
Having a shop do this would be very costly, pretty much close to 700 dollars.