I had to do it once. :'( To the best I can remember, this is what I did.
1. Disconnect from tow vehicle.
2. Lower tongue jack as far as it will go.
3. Lower rear corner stabilizer (on side of flat tire) as far as it will go, even raising the rear of the trailer if it can.
4. Raise the tongue jack as high as it will go, until the tire is off the ground.
5. Lower the front corner stabilizer (on the side of the flat tire) as far as it will go to help raise the tire off the ground. :P
If you are on uneven terrain, you may need to use blocks under the stabilizers for height and stability.
When you get home, enroll in a ERS so you can make a telephone call the next time a tire goes flat and you can watch someone else change it for you! :