how hard is it to change valvesprings?

 

depends on your mechanical aptitude and whether the engine is apart or together.

engine together:
rent a valve spring puller from the parts store designed for removing them while the engine is together. rotate the cylinder your changing to the bottom of the stroke. Usually just toss a straightened metal coat hanger down the spark plug hole and watch for it to go in as far as it will and stop. Then start dropping a long piece of string down in there (about 6ft will do) then rotate up as far as you can easily so the string sets on the valves so they wont drop in when you remove the spring. remove/replace spring with puller and repeat for the other valves on that cylinder then rotate back down, pull the string out, and move to the next cylinder.

engine apart:
rent one of the BIG c-clamp looking pullers from the parts store and put the beveled side on the spring and the flat adjustable side on the valve face. Push with all your might, take off the retainers, release the clamp, remove/replace spring, reclamp, replace the retainers, release the clamp, and move on.