Don't take this the wrong way, but best to skip upgrades on this one and ride it "as it is". Unless, of course, you have some parts sitting in your parts bin. The 26" steel rims, steel one-piece crank set, steel stem and handlebars, stem mounted shifters, safety levers, and low-end components make it a bike that doesn't warrant the expense of upgrading. However, it is probably the perfect "campus" or "station" bike and has solid utility value. If you did want to do upgrades, the following are a possibility:

alloy stem, possibly alloy bars, Dia Compe side-pull brakes, and that should about do it.