Why are you changing the lives? Did you make the map and mess up? If you made the map you should know.... beacuse theres many ways to do the lives.... Now if your editing someone elses you will have to look around, i just hope your not rigging it so its to easy becuase that makes TDs suck.
Anyway here are a few types i might use so mabey look for these.
A bunch of units that are killed in a region, when no units are left you lose (Starcraft style (ild be surpiresed to see this one Starcraft not having any variables))
A variable named "lives" subtract from it when its 0 you lose.