when changing a tire on my trailers with leaf spring suspensions in soft dirt/sand I use a 12 ton shorty hyd jack under the axle tube next to the U bolt. Simply raise one end of the axle enough to do the change.The jack has a 10" X 10" wide base for side of the road work. The jack stays in my truck when on the road.
If I'm on concrete by my garage I use my floor jack raising one end of a axle enough to make the change.
A floor jack can weigh 80-90 lbs and gonna' be a bit heavy for lifting it off the ground under a trailer.
Some folks like to pull one tire up on a ramp hopefully raising the flat tire off the ground enough to make the change.