How can I get a defualt judgement vacated/set aside

I was served with a default judgement on 7/20/2016 by the Schenectady county sheriffs office. i had no prior knowledge that I had a judgement against nor was I aware that I had to appear in court about said judement. The plaintiff is a debt collector called unifund. I have trying to find out how to get the judgement vacated so I can have my day in court, but know one in the Schenectady city courts will help me.