1) Send them an updated lease if one is not in effect. I would imagine you did a one-year lease. If they don't sign the updated lease, they are in hold over. You must give them at least 30 days to sign the new release. NJ allows for a penalty of double the rent, if a tenant holds over.
2) Send them a Pay Rent or Quit notice. This has to be done 30 days prior to the court date. It should state how much rent is due. Send it certified mail.
3) Go on line and find the NJ forms for eviction for the county of where they live. I think they're under Special Civil or Landlord/Tenant. Fill out the form and send it to the courts ASAP. You'll need to send along a copy of the Pay Rent or Quit notice. They'll be served by the courst. You'll need to make sure the court date is 30 days later than the Pay Rent or Quit notice.
4) You will either have to go to court...or you'll need an attorney to go on your behalf. NJ is a "mediation" state, so they'll ask you/your attorney to go to mediation. Basically, if they have the rent money they can stay and must pay you or make arrangements to pay some. You can opt to make them pay it all "today" or go before the judge and have them evicted. They get about a week to clear out on their own or you then have to contact the sherrif's department of the county to meet you or your representative and have them "locked out".
If they are not paying rent, this is pretty easy. If they are just late, and have been paying rent and late fees, then it will not be so easy as you are still getting rent. Make sure your lease states a good late fee like $50 - $100 and make sure you're getting a good security deposit (NJ allows 1 & 1/2 times the rent), in the event the default on the lease.
Since you are not in the area, I would use yellowpages.com or simply google property managers in that area and they would be able to handle this for you.
Hope this helps!