Heartland, Dexter (axle mfg), and Lippert (frame and axle mfg), all say to jack up the frame. This is more difficult than jacking the axle or suspension components, but you won't cause damage. You should be hitched to the tow vehicle and have it chocked.
You'll also probably need wood blocks to spread the load above and below.
And you'll need a bottle jack that can lift the weight. If you have a 14,000 # trailer, you could be lifting about 6,000 # on each side. If you use a 6 ton or 20 ton jack, you'll find it easier.
