How can I stop cutting myself ): ?

Ive been doing in since January this year and when I started I was doing it because I was depressed and sad, I lost my grandad, my friends left me and I didn't like my school. But now I have new friends and Im getting used to the school (although not fully over my grandad, we were always very close) but I cant stop myself cutting, I read on the internet that it gets addictive and its hard to stop, I need help! How can I stop?!