The pedals on your grand piano are used to change the tone of and sustain notes as you play. Most American grand pianos have three pedals: the "una corda" pedal (the leftmost), the sostenudo pedal (in the middle) and the sustain pedal (on the rightmost). Replacing any one of these pedals involves partially dismantling the piano cabinet.
Removing the Pedal Assembly
Crawl beneath the piano's keyboard. Locate the two metal latches on each side of the kickboard, which is the main panel that runs across the piano cabinet. Disengage the latches and tilt the kickboard upward to reveal the pedal assembly inside the cabinet.
Find the three wood or metal rods attached to each pedal by a hand screw. Loosen the hand screw attached to each pedal by hand. If they are too tight, use a wrench to loosen the hand screw. Unscrew each screw from the pedal assembly.
Lift the off each pedal. starting with the leftmost pedal, and slide it out of the way. Repeat this to remove the middle and rightmost pedal blocks.
Examine the pedal assembly to see how it is fastened to the piano cabinet. In most cases, it will be secured by a few screws or bolts. Unscrew the pedal assembly's mounting hardware as necessary. Grasp each end of the pedal assembly and slide it out of the piano cabinet.
Installing the New Pedal Assembly
Slide the new pedal assembly into the piano cabinet. Align the pedal assembly's mounting screw holes with the screw holes inside the cabinet. Fasten the assembly to the cabinet with the screws or bolts included with the pedals.
Align the left-most pedal rod with the threaded screw-mount on the left pedal. Slide the rod onto the mount. Then place the washer included with the replacement pedal assembly onto the screw-mount. Fasten the rod to the pedal with the nut included with your pedal assembly installation kit.
Repeat this process to attach the pedal rods to the middle and rightmost pedals. Pull the kickboard closed and secure it to the piano cabinet with the latches on each end of the piano.
Have a professional piano repair technician adjust the pedal assembly's tension properly. Doing this yourself can result in breaking important piano parts.