Some of them use 15mm wrench. Some require a thin 15 mm wrench. Some can be done with a 8mm allen wrench.
Right side pedal is standard thread. Righty-tighty Lefty-loosey.
Left side pedal is left hand (reversed) thread. This means "Righty-loosey" "Lefty-Tighty"
Hope that helps.
Right on gmats!
I just wanted to add that the allen wrench would be used on the backside of the arm, if that's not immediately obvious.
Be sure to use some anti-seize on the threads when reinstalling! (or some grease)