... particular notes to trigger changes up, or down); or PC keyboard keys; or - for touchscreen laptops - there are big, fat buttons to press.
Midi Patch Changer could work with other, similar programs, where you have a sequence of "songs" (ie. sound patches) that you want to be able to move up and down through. Midi Patch Changer is essentially like a midi translator - take an "incoming" midi message, and use it to trigger a number of "outgoing" midi messages.
Check the Wiki for more information.