Your local auto parts store should have a valve spring compression tool to rent or borrow (even Autozone:) After removing the tension the valves should slide and spin freely.. if they do not you have a carbon build up issue. If you are this far into the head you may just want to bring it to a machine shop who will do the seats and install new guides, springs, seals etc for you. If this has not been done on this engine before, it is well worth doing well.
