Replacing a showerhead is one of the easiest home upgrades there is — no shutoff needed, just a wrench and a few minutes — and a new low-flow head can improve pressure feel while saving water.
Remove the old head
Unscrew the old showerhead from the shower arm by hand, or grip it with a wrench (pad the jaws with a cloth to avoid scratching) while holding the arm steady so you don't loosen it inside the wall.
Clean and tape the threads
Clean old tape and debris off the shower-arm threads, then wrap plumber's (Teflon) tape clockwise a few times around the threads. The tape seals the joint so it doesn't drip at the connection.
Install and test
Thread the new showerhead on by hand, then snug it a little more with a padded wrench — don't overtighten and crack it. Run the shower and check the connection for leaks; add tape if it weeps.