How do you tell a college you aren't going there after sending the deposit?

I sent in the deposit to go to one school, but then I got into another school that I'd rather go to off the waitlist after May 1. Is there a particular way I go about telling the first college I'm not going there? Do I just call them, and thats it, or are there other steps? The colleges website doesn't really say|||You want it in writing so there is no confusion about your name or intentions. You could send them an email or letter in the mail.