Jack it up a little bit, let it open the bleed valve to let air out.
It will trip on suspension fault as it's trying to lower the car but it's lowering as it's on your jack.
Reset fault, and cycle key to make it open the bleed valve again. Sometimes you need to cycle the battery for this.
Once you can feel on the bag itself that it's not hodling pressure (it'll be just like any rubber bag by then), turn off the air system in the trunk on the left side behind a cover.
Jack it up and put it on stands.
Remove the air pressure tube going into the shock by a locking thingy or a twist, can't remember.
Replace the strut just like any other strut.
Lower it, turn on the air system in the trunk, cycle the key a few times to let it pump up the bag.
Done.
