Jacking up the trailer to change the tire

So I hooked the boat up today to take it to Tommy's to get it dewinterized. Well I made it about 50ft before I realized the right rear tire on the trailer was completely flat. Weird thing was it wasn't flat sitting on the driveway. Well I turn around and get out my air compressor to fill it up. The valve stem was broken where it meets the rim. So now I need to jack up the trailer and get a new tire put on the rim.

So my question is what is the best way to jack up the trailer? I have never had to jack one up before. Should I go buy a floor jack? Should I use the jack for my truck? I am leaning towards the floor jack right now as they are just a good thing to have around. Is there anywhere special I need to place the jack? Thanks for any help you guys can provide!