Converting a Legal Triplex into a Legal Quadplex in New Jersey

[Antonio Cucciniello]

Hi! I own a triplex in Ewing, NJ.  The previous owner at one point in time turned the basement into his home while in the middle of a divorce.  He built a bathroom and a bedroom.  Its not entirely finished, but if I finished the basement it can be a one bed one bath unit.  How do I go about making it a legal Quadplex? Who do I go talk to about this?