Since the upgrade I can no longer login to my admin, it is saying I entered wrong password or username.
Since the upgrade I can no longer login to my admin, it is saying I entered wrong password or username.
Check out this (https://www.zen-cart.com/tutorials/index.php?article=2) tutorial; assuming that you can access your store's phpMyAdmin, it shows how to add a default admin password to allow you to get back in.