There are mutliple artists by this name (none of which are the same as .upset, Dj UPSET, or The Up Set):
1. Upset is a Los Angeles-based band fronted by Ali Koehler (Vivian Girls, Best Coast) who is backed by Jenn Prince and Patty Schemel (Hole). Their debut album is set for a Fall release on Don Giovanni records.
2. Upset was a British power pop band. It was made up of Archie Brown (vocals), Robert Jones (guitars/vocals), Rolo McGinty (bass/vocals), Dave Berk (drums). Read more on Last.fm