There is no separate comparative form of "upset" like there is for adjectives like "big" (bigger) or "happy" (happier).
"Upset" is an adjective that is irregular, meaning it doesn't follow the usual rules for forming comparatives and superlatives.
To express a greater degree of upset, you would use "more upset" or "less upset".
For example:
* "She was more upset about the news than I was."
* "He was less upset after talking to his friend."