I've seriously lost track of how many times I have answered this question previously on the forums. :)
I wrote an article about it a little while ago, which is located here: http://www.tmib.net/content/recover-reset-admin-account-passowrd-osticket(http://www.tmib.net/content/recover-reset-admin-account-passowrd-osticket)
Short version is you have to update the password in the database.