in act two the protagonist struggles with and resolves the goal set at the end of act 1. act 2 ends when the concrete goal began in act 1 is resolved, made irrelevant, rededicated to or abandoned. Another or the same concrete goal is begun or rededicated to.
in lord of the rings Frodo succeeds in getting the ring to Rivendel, thus resolving his first goal. His new concrete goal is to destroy the ring by dropping it into a volcano.
on to act 3