If you don't know, hire and electrician. You are only allowed so many tandems by code. We just did a reno where they put the 60a charger circuit in the main panel, so we did not have room for the new reno circuits. My electrician pulled the car circuit out, and ran a line to a new sub panel for it. Which freed up space in the main panel. The idea being having room for any future circuits in the main panel, while feeding the car circuit and any future basement or garage circuits from the sub panel. If they get a second electric car, they are set up for an easy solution. My electrician only charged $800 for the sub panel and moving the existing care circuit.