I want to replace a 110v water heater with a 220v water heater but not sure how to hook it up

What size is the present wiring? What size (amperage) and type (single or double) is the present breaker?

You run the new appropriate circuit to it. You cannot use the old one.

It is most likely a 240 volt heater and will need a new service.

Turn off the water heater circuit breaker. Check everything, and I mean EVERYTHING (including lights) else on the premises and tell us if something else quit working also.

Attempting to determine if this is a dedicated 120V circuit