I have a delta bathtub faucet, shower with 2 handles. I'd like to change it to single handle. What is involved in changing it out? I have chrome but want to put in rubbed bronze.

The easiest way is to get a remodel cover plate such as this one. Moen 1920P Remodeling Cover Plate For 2 & 3 Handle Tub/showers

Use plumbers putty to seal.

This is another way of doing it with simple hole covers. Sink accessories - faucet hole covers - from FAMOUS PLUMBING SUPPLY

Then you have to make a big hole in the shower. That depends on what your shower walls are made from.

Then there is the question of access from the back.

Then there is the question of what kind of pipes are we looking at.

You may have to install new ball shutoff valves.

You'll need support for the shower valve. The allthread pipe clamps and bases work great.

Sweating the shower connection will likely require a heat shield and will be your toughest connection.

A short pipe cutter will probably be necesssary if you have copper pipes.

So, instead of answering your question, I have a lot of questions for you. There is a big difference when using a shower surround vs. ceramic tile.

I have a ceramic tile shower/tub combo. It has a Delta 2 handle shower/faucet set up. There is a covered but-out behind the tiled wall for access to the pipes. This is the original hardware used when the house was built in the late 70's. I really wanted to use the fixtures I have but change them to a trim kit in rubbed bronze. I was told by Lowe's that Delta does not make a trim kit for this model. Can I use another brand if I could find one that has 2 handles? And do you know where I could find one?
Thanks

this model =
copper pipes (T/F) =

A lot of the single handle shower cntrols have standard dimensions. Take it to a plumbing supply house for a fit.

Finish of the material doesn't matter. You can always have it plated. There are online places that will do it and there may be local ones too.

You can also have the original ones plated too from a company such as this one: International Silver Plating ~ Repair, Replating, and Restoration

Your house, though could have more value with a modern anti-scald single handle shower valve. They are also more convenient.