I currently have a 100 amp main in my house and want to add an electric hot water heater. This requires a 50 amp breaker. I already have a 220 a/c and clothes dryer. Do I need to go to 200 amp service, and if so, what do I need to do to accomplish that?:confused:

You almost certainly will need an upgrade to 200A.

The best way to accomplish this is to get several quotes from electricians and pick the one you are most comfortable with.