I want to replace the shower handles and valves in my bathroom. My diverter valve is leaking and needs replaced and I thought I would replace the hot and cold as long as I am at it. I have a 3 handle system. Is there an easy way to figure out what brand it is? I can't seem to get the valves out using a deep socket wrench can't find a nut. Was there a brand 15-17 years ago that was soldered in?

"Was there a brand 15-17 years ago that was soldered in?"

We soldered them all in 15-17 years ago and still do.
I've put up a three handle shower valve,(see image) to help you. All three handled shower valves are pretty much built the same.
Turn the water off and remove the stems. Take them into a plumbing repair shop and ask them to replace them. Good luck, Tom