After you remove the half shaft from the intermediate shaft, your pretty much home free now
Next, you just have to push the new axle onto the the intermediate shaft. Line up the splines on the shaft with the one's on the new axle. you should be able to do this by "feel" though the axle. remember to kind of work it on there, using a bit of a rocking motion.
once you get the axle onto the intermediate shaft, you then need to put the other end into the wheel hub. same as before, make sure to line up the splines so it'll slide right into place in the hole. It may take a little working about to get it into the hole where it belongs. Then you just have to reattach the wheel hub to the strut, and if you have ABS brakes, to attach that bolt back to the strut also.