Where can I cancel my Club subscription?

You can cancel Club subscription easily anytime from your My Account page > Subscriptions: https://yithemes.com/my-account/my-subscriptions/ 

And switch the auto-renewal button to OFF.

Then you should see a modal window where you can confirm the cancellation:

If you click on "Yes, I want to cancel the subscription" you have completed the cancellation.

IMPORTANT: You cannot reverse a cancellation, and would not be able to join again this plan, as it is no longer available for sale. Please, make sure you only do that if you don't want to use the Club anymore.