Turn off the shower and let the water stop completely
Unscrew the shower head from the shower arm
Inspect the inlet for a plastic flow restrictor
Remove the rubber washer if needed to access the restrictor
Pry out the restrictor with a small flathead screwdriver or needle-nose pliers
Remove any retaining ring or screen holding it in place
Reinstall the washer and screen
Screw the shower head back onto the shower arm
Turn on the water and check for leaks
Confirm the flow meets your preference and local regulations