If your hosting has cpanel click on the mysql icon then scroll down to the bottom and you will see a link to phpmysql click on that and it will take you to another page, there you can choose your database and them run the query.
As for not being able to run it from admincp I think, and I might be wrong, but edit your includes/config.php and find
// ****** USERS WITH QUERY RUNNING PERMISSIONS ******
you will see $canrunqueries = '1';
If you setup the forum then you should be user #1 but if someone set it up for you then made you a member you will have a different number.
Also make sure $superadministrators in the same file has your number in it.
Hope that works for you