The valves themselves generally don't need to be replaced on these, unless it has dropped a valve seat.. but in that case the head, piston, and most likely cylinder wall will be damaged beyond repair if this has happened.
If the head gasket itself has blown, then you NEED to send the head out to a machine shop who can do the proper testing with the proper equipment to make sure the valve seats, valve seals and valves are in good condition, and that the head isn't warped or cracked.
It is VERY common for a head to warp/crank on these, ESPECIALLY if it has been overheated, or run low on coolant. This is not something you're necessarily going to be able to tell by looking at it, and if you reinstall a warped/damaged head, it will just continue to leak into the lower end.. best case scenario... you'd have to do the whole job all over again. Worst case scenario - you end up with more damage than in the first place!
So you see, coming on here and asking us how to change the 'valve cylinders' is the wrong thing to do, as there is no such thing. In the head, there are lifters (and their retainers), valves (and valves seats and valve seals), rocker arms, the camshaft, attaching hardware, and of course, the valve cover.
If nothing else, invest in a HAYNES MANUAL... or maybe even an online service such as alldatadiy.com