I have a shower with a hand held and overhead... the overheads flow is 1/2 of the handheld. I have ordered the new cartridge and it arrived but I am not sure how to change it. We have been waiting for the plumber to call for a few weeks and I am losing patience. A friend said this was easy to do and not to wait... is it so? It is a rohl system. Thank you in advance.

Rohl has screens in their shower heads and body spray heads that limit the flow. You may have to simply disassemble and rinse the screens and reassemble. Good luck however. It took me over an hour to figure out how to assemble one of their body spray heads during an install and I had the instructions. Their instructions are far from accurate and you will need a special large allen wrench