Have an older 30 gal. heater and need to replace element but store's I have gone to say that I need to replace heater. Would it hurt heater to put 4500 element in if it says 3500? 240-220 power going to heater?

Yes, assuming you have 30 amp breaker and 10-2 wiring.
Check physical size. However, a 3500 watt element should be readily available.