Are you taking about the built in divertor part of the shower body or the type that is part of the tub spout?

The diverter is on the tub spout.

I have the problem with most of the water coming out of the bathtub spout when I push the button to get the water diverted up to the showerhead. How can this be fixed? Do I replace the entire bathtub faucet, or is there a way to just replace the part that is supposed to send the water up to the shower head?

you'll need to buy a new spout. standard ones are very inexpensive and easy to install. apparently you can't just buy a replacement stopper for the inside.

Thanks for your help. Any advise on how to get the old, defective faucet off? It is tight on the wall, and sealed with a thin bead of calking. There seems to be a little screw on the bottom side of the faucet. Do I unscrew that, and then yank the faucet off the wall or what? Thanks!

instructions should come with the new spout, however in case it doesn't...

there is a small screw at the bottom that you need to remove (tool might come with the new one). then break the seal against the wall and it should come of easily. its been a while since i replace one, but i think you just pull or twist gently to get it off. put the new one on, replace the screw and reseal.

Thanks for the info.

I used an allen wrench to remove the little screw on the underside of the old faucet, and then the faucet pulled off easily.

Thanks for your help!