Upper division and lower division classes are both types of undergrad classes. I've heard that its better to take upper div classes if you're trying to boost your GPA. I'm actually thinking of doing the same thing this summer, but at the same time I might also take some lower div classes because they're easier. I know ppl are going to say that adcoms won't look favorably at that, but in my opinion I think its better to take a class that will definitely boost your GPA than a class that you may not do so well in. I'll probably take some upper and some lower div classes.