I recently renovated my shower and the pressure in the new shower is consdierably lower than the pressure in my upstairs bathroom which was an addition to the original house but still more than 20 years old. I wuld like the pressure in my new bathroom to be the same as the upstairs. I have removed the flow regualtor which helped some but is there anyway to make it better. If I change pipes, do I need to change every pipe from the water lead right to the shower head or is changing the pipes that run into the bathroom good enough. Any advice would be appreciated.

Until the Expert comes along with more:

Double check your cartridge or seats... and the screen in the shower head for crud that might have gotten flushed into them when the water was turned back on.

"If i change pipes, do i need to change every pipe from the water lead right to the shower head or is changing the pipes that run into the bathroom good enough?"
Before we can advise you about your pipes we have to know what you have, copper, galvanized or plastic? How old are they? In the meantime follow Ricks advice. Shut the water off to the shower and open up the valve. C heck and clean the inlet ports on the cartridge and before you reassemble flush out the supply lines. Good luck, Tom