We just recently remodeled our bathroom and made a few changes in the pipes going from the basement to the second floor and since that time we still have very hot water downstairs but the shower water is only lukewarm. Please help!

How are the rest of the fixture sin that bath, still hot? Most likely some debris came loose during the remodel and is not clogging the hot inlet on the valve. Open the shower mixing valve and clear the debris. I won't go into any more detail unless you ask, if you did all this work yourself you likely know how to talke apart the valve. If not, let me know