To remove a valve, you will need to remove the cylinder head and inspection cover. It also helps to remove the intake and exhaust manifold, but it's not absolutely necessary. You will need a spring compressor to relieve the tension on the valve keeper. The attached pictures show the two styles available. The smaller wedges between the spring and block and the handle is turned to compress the spring. The larger version, which I use, seats the upper half on the top of the valve and the lower half at the bottom of the valve spring. When the handle is seated, it relieves spring pressure.
Using either one will work, but be careful because once tension is off the spring, the valve keepers may fall out. The keepers are small and easily lost so have a small magnet handy to fish them out as you take the tension off the keeper. I should mention this job is best done with two people but you can do it alone.
Once the keeper is out of the way, remove the compressor and lift the valve out of the guide. The spring and cap, if being replaced, can be wiggled out the opening in the block. Pay attention to the ends of the spring because they are different (I dab the upper end with white paint). Install the new springs exactly as the old ones came out. Replacement is the reverse of the above.
Before you install the new valves, check the seats for pitting and undue wear. If the seats are worn, you'll end up with low compression and poor performance. New seats can be installed but it'll take an engine rebuild shop to do that work.
Poll