When to stop bluffing?

[Solami17]

Against the 55 hand, check the turn for a free card and fold to an unimproved hand if villian bets the river here.
or if your hand improves (catching a K or T) you can call a bet.

Or you could also reraise in a bluff attempt. (although i dont know if this would work agianst this guy in a freeroll tourny since he has done this several other times)