Troubled,
angry,
sad - in some way not in one's
preferred emotional state.
This can be a state... ("Pseudo_Intellectual is upset about his desk chair's wobbliness.")
or an action... ("Jessicapierce has upset Katie Hyde and made her cry.")
Upset can also describe the physical state of an object in the same way: something that has been knocked over, which has toppled, which has been spilled. If you upset your glass of milk, you'll have milk all over the floor (to cry over, knowing you!); if a statue is upset, I expect it's lying sideways in the park.
On the other hand, and somewhat archaically, it can have the opposite meaning: to set something right, to set something up. If you upset the topsy-turvy picture frame, you could setting it up straight. However, most people are apt to interpret it as knocking it over further, unless they happened to witness the act, so it's probably best to avoid this use in conversation with those younger than Webster 1913.
Pseudo_Intellectual wishes to add that despite my example, he is not in fact upset by his desk chair and never has been (oh yeah? why'd you get a new one?) and would like to add that it would be more appropriate to list its wobbliness under the physically upset category, which it was wont to do to the untrained.