In your profile (at the top of More or Settings), Delete account removes your Macuta account, the backups on the server and the data on this device. To confirm, you type APAGAR and then the 6-digit code sent to your email. You also lose your paid plan, with no refund for the time left. Your other devices keep the data they already have, but without an account.
This can't be undone. If you want to keep your data, export a data file first.