Place the ham in a large roasting pan with a rack, tent it with foil, and bake for 2-2.5 hours (longer depending on the package directions).
In a small sauce pan over medium-high heat, mix together the brown sugar, mustard, vinegar and root beer and bring to a boil. Reduce to a simmer and cook until reduced and thickened, about 15 minutes.
After about 2 hours, remove the foil and brush the glaze on the ham in 20 minutes intervals (put the ham back in the oven, uncovered, in between) until it’s nice and glossy. Remove from the oven and allow to rest 15-20 minutes before serving.