If you are a teacher that already has an account and need to add another Access Code to your account to gain access to additional content, log into your account. In the top-right corner, click the arrow to access the menu, then click "Account."
On this page, you can see all of the Access Codes you're already redeemed. At the top of the page, there is a space for you to enter your new Access Code. Enter it, and then click "Add." If your Access Code is valid, you will gain access to the additional content.