Open up the lower front panel of the piano. If you look under the keybed there is probably some sort of latch mechanism. Unhook the latch, and tilt the panel out toward you. You may then remove the panel and set it aside. Examine the pedal mechanism for the source of the squeak. Stay away from WD-40. Piano tech's often carry graphite powder for lubricant. As a substitute you can use the graphite from a pencil or artist graphite stick (you can get in an art supply store). If the source of the squeak is a rubber grommet, you could also use scrapings of candle wax as lubricant. Take note that the vertical rod connecting the lower pedal mechanism to the action may fall out of place as you play with it. This is not a big problem, you just have to note where the connection points are before it does fall out. You may have to remove the top panel in order to see where it connects to the action.