You need to remove leg from caravan to do the job so you have to hope you can undo the 2 13mm nuts that hold it on. Once off you need a bench vice to hold leg. Remove pin that holds screw so you can unscrew it out, then prise leg apart to remove old block & drop in new.
It depends on whats above the corner leg, is it under the shower tray or the cooker or fridge. if it is you will have a problem?? you would have to remove whats above it to get to the bolt heads and then they may not have bolt heads but a screwdriver slot.
it is possible to replace the screw block while the leg is still on the van if you can get enough space to work on it.
look carefully at this picture, if you have this pin and spacer, look just behind the the bolt head where you attatch your winding handle.
if you have and you soak it in WD40 for 24 hours you might be able to knock it out using a pin drift.
if you have this pin and can remove it the threded bar will then be able to remove the bar and with some manipulation fit a new screw block, for app £8
there is a hole directly above and below the pin to use for driving out the pin.
if you can remove the leg from the caravan its easy enough for the average DIY person