If your website has been compromised, you might need to change the administrator password for your website application (or Content Management System/CMS).
The process for this depends on your application, the situation you're in, and your familiarity with different website tools. One common method of changing your administrator password that works for every CMS, though, is changing your password through phpMyAdmin (Web & Classic / cPanel / Plesk / Managed WordPress).
|WordPress®||Resetting Your Password|
|Joomla!||How do you recover or reset your admin password?|
|Drupal||Recovering the administrator password|