When you subscribed, you should have got a homepage inbox message.
If you go to your account page at http://www.chess.com/home/account.html where you will see a link toward the top to cancel/end your premium membership subscription so that it does not auto-renew on the next scheduled period.
I purchased the platinum membership about a month back just to try out some of the features it offered. without ever knowing that the subscription would automatically renew itself every month (it never said that anywhere). As the title says, how do i unsubscribe to chess.com? I don't want to spend 8 bucks a month for online chess, especially when I much rather prefer OTB.