It should be in the manual. If you don't have one here is a link to one:
I did this within the first couple days of ownership and the instructions worked. I will say, however, that the instructions are misleading. I believe it says something along the lines of buckle and unbuckle the seatbelt six times or so but I haven't read the instructions in about a month. When I got to the last one nothing happened so I kept going. It took a couple more times before it triggered the system. So my recommendation is, ignore the number of times to buckle and unbuckle, and just keep doing it until you see the seatbelt light flash indicating the system has been disabled. If you don't get it at first keep trying. It will work.