There is no way we can tell what your wiring looks like, but normally a water heater and its circuitry is adequate for 4500 watt elements. The wiring is "beefed up" for 5500 watt elements, however. Replacing the upper element with a larger one, however, usually does nothing to increase the heater's performance, BUT, when the upper element fails, it USUALLY means the lower one is bad also.