To simply change your password, log in to your administrative backend and go to Profile->Account Settings

 If you have forgotten your SMF administrative password, you can easily retrieve it from the “Forgot your password?” link on the log in page – you will receive a link, that will force password change, to the e-mail address associated with your administrative account.

An alternative way to change the password is directly from your database. To do that, open your cPanel->Databases->phpMyAdmin->your SMF database->smf_members table. Locate your administrative user and click on its edit button (a small pencil icon). Find the “passwd” row and input the followin string in place of the one that is already there:

449ed97bdef672c3aadc98dcdaa63fe9d357f8f1

This will reset your password to pass123 . You should then log in immediately and change your password to a more secure one.