Change Magento Password from Admin Panel.

System > My Account
If you would like to change your default password and user name, the security of your password has been compromised, or you would just like a new password, it can all be accomplished very simply with Magento Go.

To Change Your Password and Username:

1. In the Admin Panel, select System > My Account.
2. Add a new password in the New Password field. Confirm your password by entering again in Password Confirmation field. You can also change the other fields that are available for you.