What must happen for a hypothesis to become a theory?

The hypothesis must be "proven." A hypothesis is just a guess or a prediction of what may happen. If the hypothesis is proven to be correct by valid data, it can graduate to a theory. However, a theory can never be technically proven, only disproven or YET to be potentially disproven.

When a hypothesis is proven by an experiment then it becomes theory.

If enough evidence accumulates to support a hypothesis, it moves to the next step - known as a theory in the scientific method and becomes accepted as a valid explanation of a phenomenon.

Hypothesis is constructed before any applicable research has been done. A theory, on the other hand, is supported by evidence.