polarity was backwards, how to fix?

On my recently acquired Super Jet I discovered the battery was connected backwards, negative ground. Judging by the size the battery clamps were set to I think the battery has been in the car backwards for some time.



I flipped it around the proper way (positive ground) but I'm reading that I need to change over the system's polarity back to normal now somehow. Can anyone tell me how exactly I do that? This is the original 6 volt system.



Thanks!

Carl