To reset the VoiceLive back to factory settings you will need to do the following 3 resets, each resetting different things:

Resetting the system parameters involves resetting all global settings not stored in presets, like in/out volume, compressor settings etc:

Hold the PREVIOUS + NEXT keys down and insert the powercable into the connector on the back.
The display should now read "VWF PSDC Firmware v0.23".
Let go of the PREVIOUS + NEXT keys and turn the encoder wheel until the screen reads "Reset sys param?".
Hit EDIT to confirm.
Wait until the display reads "Clear/reset done".
Remove the powercable from the unit to turn off the VoiceLive; put the powercable back into the connector to turn it back on.
Clearing all presets deletes all settings stored in the presets, like settings for the pitch-correction, the harmonies, the effects etc:

Hold the PREVIOUS + NEXT keys down and insert the powercable into the connector on the back.
The display should now read "VWF PSDC Firmware v0.23".
Let go of the PREVIOUS + NEXT keys and turn the encoder wheel until the screen reads "Clr all presets?".
Hit EDIT to confirm.
Wait until the display reads "Clear/reset done".
Remove the powercable from the unit to turn off the VoiceLive; put the powercable back into the connector to turn it back on.
Clearing all songs deletes all settings stored in the songs in SONG MODE, like the chord/root and preset chosen for each song step in each song:

Hold the PREVIOUS + NEXT keys down and insert the powercable into the connector on the back.
The display should now read "VWF PSDC Firmware v0.23".
Let go of the PREVIOUS + NEXT keys and turn the encoder wheel until the screen reads "Clr all songs?".
Hit EDIT to confirm.
Wait until the display reads "Clear/reset done".
Remove the powercable from the unit to turn off the VoiceLive; put the powercable back into the connector to turn it back on.
That's it; your VoiceLive has now been reset to full factory settings.