How do we repair or replace a shower diverter? Water continues to come out tub faucet and only a small amount of water comes out shower head.

Eddy... what is the name on the faucet? About how old?

NO name anywhere and about 236 years old...

Must look like this. Purchase seat wrench and set of tub faucet wrenches. Remove handle and stem covers. Remove stems, may as well do them all, not just the diverter, remove seats. Take to home center or plumbing supply. Purchase new stems or all of the parts you need to rebuild. You can probably rebuild faucet stems but diverter has some funny parts. Probably beat to purchase new one. Be sure to take seats with you. There is 1001 different sizes, shapes and threads. If you rebuild get some plumbers grease and grease stems and they will be like new. Probably want get new washer screws if you rebuild. If you have problems removing handles note the picture of the faucet handle puller.