You can't change it in the emu. The standard release comes with a not aspect correct 320x240-resolution (ugly widestretched).
Thus I released four modified versions in 2008 with four different resolutions:
- 320x200 (for most games)
- 384x216 (for Turrican)
- 414x240 (for some games like Rodland or Arcade Pool)
- 480x272 (for Superfrog and Pinball games)
In those versions you can move the displayed screen vertically with R+dpad up/down (if something is cutoff).
The majority of games aren't fun with PSP UAE4All, but there are exceptions: I've completed Wings (works almost fullspeed) with the 320x200-eboot.
Also Stunt Car Racer, Targhan and Robocop work good.
Download here:
User mode versions
Or, if you have an old phat 1.5-firmware compatible PSP you can get the
kernel versions.
There is a txt-file included describing various added control changes.