If you can, get the machine on a level spot and on a hard surface (concrete or asphalt) , get a floor jack and try to center it under the skid plate, jack it up so it is just resting on the underside of the skidplate, remove the mounting bolts, and SLOWLY lower the jack, the skidplate may slide if it is not balanced so be careful. Check the valve then reinstall the plate. Good luck....
D Reed, Tags is right on about the floor jack!! I have a flat furniture dolly that I put on the center head of the jack. Only other tip is to make sure to use a alignment punch thru the skid plate holes to help line up the bolt holes. I would put in by hand to make sure to get them started straight. It's easy to cross-thread them if you're not careful.
Good luck!!