Level ground - no complications?
You can only brace - and lift the sag out to level the ladder frame points once you lift the frame from the correct points. Its a C-channel and will collapse, bend, distort, stretch. There are dozens of posts here on the subject - the search function is your best bet to get the background to ask the right questions - here's two I've contributed to. Oh yeah, the risk is all you - don't even trust we can see how and what from our PC keyboards
The vertical steel sheet that the axles mount to is the only place to safely lift the trailer from. There is room for 6x6 wood blocks to crib up the jack, and you will need a block of wood with the grain oriented across the plate steel length to keep it from splitting from the knife-edge effect, and you will need blocks to chock it up besides the jack blocks. You can't lift much at one time, a 4x4 height at a time then safely block it up, then go to the other side... blah blah.