Pedal Repair and Replacement

Pedals can be damaged by direct contact with a rock, or by the force of your weight (for example, jumping the bike off a ledge after one too many Powerbars). If the pedal wobbles or hangs up as you pedal, it needs to be replaced. If only the cage is bent, you can often repair it.

Or, perhaps you want to swap the pedals for a specific purpose. Stunt bikers usually ride on platform pedals. For those rock garden bumpfests, you want lightweight pedals that lock you in, for example SPD pedals. For winter riding, or combo riding, where you want a platform plus a clip-in, you may swap your usual SPD pedals for a downhill pedal, where a toothed cage surrounds the clip-in.

To repair a pedal cage, remove any reflectors from the U-shaped cage. 
To repair a pedal cage, remove any reflectors from the U-shaped cage. 
Repairing a Pedal:

Make sure the pedal rotates properly, and that the spindle and mounting aren't bent. If the main body of the pedal is damaged, replace it.

To repair a pedal cage, remove any reflectors from the U-shaped cage.

Remove the cage from the main pedal body. The cage usually attaches to the pedal body with phillips-head bolts.
Taking the cage off a "flat."
Taking the cage off a "flat."
Do the minimum necessary. If you bend things around too much, the metal weakens.
Do the minimum necessary. If you bend things around too much, the metal weakens.
Using wrenches, or a vise, or a hammer, or whatever, reshape the cage into its original configuration. Now bolt it back into place.
This is a platform pedal, used with ordinary shoes. A toe-clip or footstrap can ...
This is a "platform" pedal, used with ordinary shoes. A toe-clip or footstrap can be attached to keep the foot on.
Replacing a Pedal:

To replace the pedals, remove the old pedal. Slip a 14-mm pedal wrench over the pedal mounting. Immobilize the crank (for example, you can lay the bike down and use your foot to freeze the opposite crank-arm. With the wrench handle aiming towards the top of the bike, twisting the wrench towards the BACK of the bike loosens the pedal.

Pedals come in right-side and left-side versions. (If the clip-in mechanism would have you sitting on the bike backwards, you're trying to insert the wrong pedal.)
This is an SPD clipless pedal. A cleat on the bottom of the shoe locks into the ...
This is an SPD "clipless" pedal. A cleat on the bottom of the shoe locks into the binding.
This is a downhill SPD pedal.
This is a "downhill" SPD pedal.
Thread the medal-mount into the crankarm. It twists so the top side rotates towards the front of the bike -- counterclockwise on the left pedal, clockwise on the right.

This photo shows a "downhill" SPD pedal. A toothed cage surrounds a spring-loaded binding. The binding pops up above the cage for click-in, but flattens when standing on the pedal without engaging the binding.