If the wheel is off, there is a nut on the speedo (left)drive side of the wheel, I'm not sure of the wrench size, but on the other side (right) there is a slot for a 17mm wrench. The nut is standard right hand thread. Remove the nut and slide the axle out. There is a bushing on the right side, the speedo drive will come off when you remove the axle. When re-installing, note the notches on the speedo drive.
You might want to consider dyna-beads for tire balance.
OharaLTD is exactly right. Once you remove the 19mm axle nut the axle should slide out. There may be some corrosion between the axle and the bearing races/inner spacer (inside the wheel hub) that needs some persuasion with some WD40 and a few cautiously applied hammer blows. Don't hit the threads - leave the nut on a few threads and hit that.