If you have a paid subscription, you will first need to cancel your contract renewal and pay any open invoices before you can delete your account.
If you are a user of a paid account (i.e., not the account owner), are subscribed to the free plan, or are part of the 7-day free trial, you can delete your account at any time.
Once you have deleted your account, any Dynamic QR Codes will deactivate, and the content will not be accessible by your customers.
If you would like to delete your account, you can do so here or by going to Account - My Account - Settings - Close User Account.