Doss Hawks1523, seems it can be either removing the remaining bail or removing the stump from the ground
http://www.lords.org/mcc/laws-of-cricket/laws/law-28-the-wicket-is-down/
http://www.lords.org/mcc/laws-of-cricket/laws/law-28-the-wicket-is-down/
laws of cricket said:2. One bail off
If one bail is off, it shall be sufficient for the purpose of putting the wicket down to remove the remaining bail or to strike or pull any of the three stumps out of the ground, in any of the ways stated in 1 above.