You've got to undo the two bolts holding the gas pedal against the firewall, then turn the pedal so that it's slightly sideways and press that retaining pin out. I seem to remember there being another bolt somewhere in there as well. Once that's done, you'll have to bend the long end a bit. We ended up drilling out the hole on the long end to make it more oblong, which made getting the STi pedals' retaining into place much easier. From there, screw down that ridiculously tiny retaining nut and bolt the whole thing back up to the firewall. It's easy.