Make sure that you get the pedestal designed for your washer. The white pedestal for the GHW9400P would be LAB2700MQ. (There are slight differences in the pedestals for different series washers. The holes in the base of the washer will not line up with the holes in the pedestal for a mismatched combination.)
First if your washer has been installed, uninstall it. You need to turn off the water. Then disconnect the power cord and (carefully) the fill hoses. Loosen the hoses first and then completely remove them. Drain the hoses into a bucket. Disconnect the drain hose from the back of the washer. Use pliers to squeeze the clamp to get the drain hose loose.
Pull the washer away from the wall. Cover the area behind the washer with cardboard and tip the washer onto its back (on the cardboard).
Pull out the drawer of the pedestal. Next snap the spacers into the holes on the top of the pedestal. (These are part of the hardware kit in the drawer of the pedestal.) Remove the shipping spacers from the front of the pedestal (behind the drawer). Remove the Philips head screw from the drawer slides and pull the drawer completely out (save the screws). Push the slides back into the pedestal.
Look at the washer and remove the feet if present. Partially install two of the hex head screws from the pedestal installation kit in the bottom holes of the washer. (These are at the center back of the washer if it is standing up.) Leave the screws about 3/8" from the bottom of the washer. Move the pedestal over to the washer and slide the keyhole openings of the pedestal over the two partially installed screws. Position the pedestal against the top of the washer and insert the remaining two hex head screws. Do not tighten completely.
Align the pedestal with the base of the washer on all sides. When it is lined up, tighten the 4 screws by reaching through the drawer opening of the pedestal. Bring the washer and pedestal back upright. Reinstall the washer (remove the packaging if this was a new install). Level (front to back and side to side) the washer using the pedestal feet (again reach through the drawer opening). Make sure that all 4 feet touch the floor. Tighten all 4 locknuts.
Pull out the drawer slides and reinstall the drawer. Reinstall the Philips screws. Close the drawer.
For pictures of the install, go to the Whirlpool support site http://www.whirlpool.com/owner_center
. Search for your pedestal and get the installation manual. The direct link for the LAB2700MQ0 install is http://www.kitchenaid.ca/assets/pdfs/literature/Installation%20Instructions%20-%208537141.pdf
I hope this helps.