I have a one handle that controles my shower and tub to turn on my shower when I pull up on handle that is on top of faucet to send the water up to the shower not much come's out of the shower head and it still comes out of the faucet are the gut's hard to replace and how do I do it sometimes it is hard to get hot water to come out of the shower head

It is very easy to fix the problem. You should be able to unscrew the faucet from the wall and the just get a replacement fromlowes, home depot or your local hardware store. Most of the pipe connections are 1/2 inch NPT. Just remove the old one and take it with you.