LFO1 and LFO2 are calculated per voice. You can retrigger them when a key is pressed ('RET') and sync them to BPM ('BPM').
LFO3 and LFO4 are global LFOs. They refer to all played voices. You can find above the mod matrix. They are usefull if you want to add movements to pads, vibrato or tremolo.
Best Regards,
Markus Feil