The Previous/Next arrows step through the eight Slots one at a time, changing the selected Part without stopping any notes currently being played. The Previous/Next arrows can be MIDI Learned, so they can be triggered via MIDI messages.
When Dual Live Mode is enabled, two sets of Previous/Next arrows will be visible. The left set will step through Part Slots 1-4, and the right set will step through Part Slots 5-8. Both sets can be MIDI learned via their respective MIDI channels.