I am trying to change my front brakes on my 04 Land Rover Discovery, I have taken the tires off and the brake caliper off, but the piston wont push in, actually one is in and one is all the way out, what do I do?
You have discovered the problem with your brakes. A sticky piston. While it is possible to repair a sticky caliper, it is also simpler to replace it outright. That is what I would do if I had the money. Whatever you do, don’t step on the brake with the capipers hanging loose. Check your repair manual to see if it gives directions for caliper/piston repair.
I too strongly recommend that you do not try to repair the calipers yourself. This is a rebuild to be performed on a bench by someone with expertise and the proper equipment and replacement parts. Simply replace the caliper assemblys and turn the old ones back in for the “core charge” reimbursement.
And, if you do not have a repair manual, I strongly suggest getting one. It’ll give you good advice on things like properly replacing the caliper and bleeding the system.