If you do a monthly membership you can cancel after one month.
Canceling membership?

There is an option for membership by the month. See http://www.chess.com/membership.html?c=navbar
If you pay by credit-card or PayPal be sure to cancel premium immediately after the star, crown or diamond appears so there is no auto renewal. Do not wait one month. You will keep your premium status for the month you paid for.
http://support.chess.com/Knowledgebase/Article/View/168/0/how-does-membership-renewal-work

There is an option for membership by the month. See http://www.chess.com/membership.html?c=navbar
If you pay by credit-card or PayPal be sure to cancel premium immediately after the star, crown or diamond appears so there is no auto renewal. Do not wait one month. You will keep your premium status for the month you paid for.
http://support.chess.com/Knowledgebase/Article/View/168/0/how-does-membership-renewal-work
That was a better answer than mine.
With some extra money from Christmas, I was considering getting a diamond membership for all the extra stuff (videos, tactics trainer, etc...). I don't have enough money, infact I only have enough money to afford the membership for one month. After that month, can I cancel my membership at any time? Or do I have to subscribe for a set amount of months?