I am single and a dependent of my parents...what should my tax exeptions/allowances be?

I am 23, single, have no kids, and my parents claim me as a dependent since I live with them. I work as a part-time host at a restaurant ($11/hour, no tips). When I started working there, in September, I claimed 2 federal exemptions on my paperwork. In April, my paycheck said "Effective this pay period your state exemptions/allowances have been changed from 2 to 0". I did not authorize this change and I dont know why it changed. Is this better for me? What should it be?