An alignment has little to do with wheel/tire size, assuming you're maintaining the same overall diameter. You can have it done before or after. Bigger wheels tend to magnify an alignment issue, but they will not be the cause of it. Unless they're so heavy that they cause undue stress on the suspension, thereby throwing the alignment out of whack. On the other end of the spectrum, if the alignment was already done, a bad tire should be replaced because it can still cause pulling or other deviations. You should get the alignment and new wheels at the same time, so you don't end up ruining your new tires.