I have a tub faucet where the cold is hot and hot is cold. It is a single knob type I believe it's a Delta. Problem is, hot water starts the knob, and goes to what is suppose to be cold, but its actually warm , because the other problem is that the knob only goes half way. How do I reverse it and get more opening on the knob?

Not sure with a Delta but with Moen you actually rotate the cartrdige a half turn, try it

Do as Ballenberb said. Rotate cartridge 180 degrees. Don't forget to turn water off for the entire house. If Moen faucet than you don't have to even remove the cartridge: here, remove handle, spin the stem 180 degrees and reinstall handle.

Some Delta faucets don't have cartridges. They have seats and springs. Can you take a picture ? Regards, Tom