Dead easy,
jack it up, support by the chassis with axle stands, support axle with a good trolley jack - remove the wheel, plastic wing liner, and dig out all the mud and crap from the top and bottom of each airbag to be changed find the R clips give them a pull if they are rusted in (most are) snap them off with a long chisel (they are abot 50p each) lower the axle on the jack to take the weight off the bag, then disconnect the air pipe by pushing in the collar before pulling out the pipe, squash up the old bag and pull it out. clean out the bags seats with emery or a file carefully seat the new baglift the axle till the bag seats properly fit new R clips trim 5mm of the air pipe with a stanley knife deburr the pipe and push fit through the collar until fully home. refit plastic liners and wheels, jack up and remove axle stands and jacks, start the car and let it pump back up. if it is slow to lift leave the pump running for approx 10 mins with adoor open to build up air in the tank - job done