Remove the G5 metal cover from the processing/cooling unit of the computer. NOTE: Apple inserted a rather fragile plastic pin that inserts through the top divider shield and clips into a tab on the hidden ledge of this CPU shield. Removing this pin, certainly voided Mac's warranty - but more appropriate for now, voids most after-market insurance plans. A replacement pin (new) is hard to get ahold of, and very few are talented and patient enough to remove this pin without damaging it. Just something to keep in mind. If you have no warranty any longer or don't care, please continue...
Pull the metal plate to the left and outward to remove the plate from the processing/cooling unit.