not sure what to remove on the location of it on a supra. but in general, changing a core plug can be tricky. easyest way i find is to use a small but strong and sharp headed screwdriver and keep tapping it in but in towards the centre aswell (to stop damaging the head/block. once you have been patient lol and got through you can carefully prise it out. be patient they can take a while, and be very very carefull not to damage the engine. always best to get a garage to do it if your not confident. once its out clean up the area with a little emery cloth and make sure there is nothing left in the chamber. i normally leave the coolant all in so it helps put pressure behind the plug. i use a socket on a small extention, the exact size of the core plug inside and tap it in will a little white grease. carefull again, dont deform the plug, if you deform it even slightly then youll have to start again. once nearly in all the way use a bigger socket and flush it in.