delete it from pgadmin  

 127.0.0.1:50784/browser

I hope you did a backup of that Database, before trying to "upgrade", or "delete" a DB and have now a way to restore its information.

PgAdmin is very useful, but when you do upgrades, you must always have the old and the upgraded versions of Odoo or Openerp) properly set up before migrating data.

Use your DB backup to restore it with a new name using /web/database/manager on the newer version, and validate if the data migration was successful, or if there was any issue between both versions.

You do have to delete the database, before you can restore it using the same name (what "restore" means in the first place). You may read this in order to get a better understanding: https://github.com/odoo/odoo/issues/13450