In order to cancel your Todoist Premium membership, you must unsubscribe through PayPal. Please use this link: https://email@example.com to quickly find the payment subscription and cancel it at PayPal.
In order to delete your Todoist account, please log in at https://todoist.com click on the gear icon in the top-right corner, go to Settings -> Account and then use the red link at the bottom of this window to permanently delete your account and all data associated with it.
If i cancel before my yearly premium membership has ended, can i still use premium for the whole year?
Yes, you can cancel your payment subscription directly at PayPal anytime and the Premium time on your Todoist account will remain for as long as you've paid for upfront.