If you need to change your password to your Administration Center: Submit a Help Desk ticket asking for a password change for the specific Username.
If you need to change your email password, you can do so by logging into your Webmail account and select Passwords & Security from your configuration menu - see the screen shot below:
If you need to change your password for your Blog, log into your Blog and select Users from the sidebar and then select the username's password you want to change. Scroll down until you see the Account Management section and enter a new password there. See screen shot below: