Hi Josh,
The left encoder from the screen changes the Bank (OB-X8, OB-8, etc.). The right encoder from the screen changes the Group (each group contains 8 presets). Once you've selected your Bank and Group using the encoders, press the Programmer buttons 1-8 to select a preset. The A/B/C/D letters are present on the legacy banks, as that was how the vintage presets were originally categorized. You can find more info on page 6 in the manual.
To reset all patches to their factory state, navigate to the 'Reset Prgm To Factory' Global and select ALL.