If you can get into your admin account (https://www.google.com/a/DOMAIN.COM/)*, you can follow the steps outlined in this link to reset your password.
If you can't access your admin account, follow the steps to reset your password by clicking on "Can't access your account?" on this link https://www.google.com/a/DOMAIN.COM/*
You will then be able to click on Reset your administrator password to access your account and then follow the steps outlined in the first paragraph of this email.
* Replace DOMAIN.COM with your own domain name.