Hi,

Am not sure from where you tried to upgrade your db. If you are using the one app free plan, i expect your odoo is hosted in odoo online. So if you need to upgrade your db to newest version of odoo, just login to your odoo.com account and trigger upgrade and it wont ask any code.

* Login odoo.com account connected with your database

* Go to the page:  https://www.odoo.com/my/databases

* Near to your db name in the above page, you will see a upgrade/upload icon, click on it

Thanks