Originally Posted by markscns

You could manually remove the directory, and the MySQL database using the MySQL databases icon in your Cpanel to remove your database.

However, the question might be, which database to delete?

If you look for the Gallery config file in the directory it's installed, typically called config.php or something similar, it will tell you the database name and database password.

If this is too complicated, then submit a ticket and ask support to do this.