Replacing bike pedals is typically an easy task. However, a number of issues can cause one or both pedals to become stuck. If the bike is old, the pedals can become rusted, making them difficult to remove. In other cases the pedals have been put on too tightly. In any case, you can remove a stuck bike pedal in just a few steps.
Apply a penetrating oil -- preferably one made specifically for loosening bike parts. Spray the oil on the section attached to the crank arm and let it sit for approximately 10 minutes. Some penetrating oils work faster than others, so follow the manufacturer's guidelines.
Determine which direction you need to turn. The drive-side pedal, which is on the right, has a normal thread. Turn it counterclockwise to loosen it. Turn the left -- non-drive side -- pedal clockwise to loosen it.
Align the drive-side pedal so that it is in the 3 o'clock position. Align the non-drive-side pedal in the 9 o'clock position. Place a 15-millimeter pedal wrench, or a 15-millimeter open-end wrench on the pedal, press down, and turn the wrench according to the thread.
Use a rubber hammer to tap the bottom of the wrench if you don't have a pedal wrench, without which you won't have as much leverage. Securing your wrench and tapping it with a rubber hammer with help make up for the lack of leverage so that you can loosen the pedal.