If you are currently a Microsoft Windows Phone Developer Center (WPDC) member, you will not be able to enter your token until your membership is within three months of expiring. At that point, you will have the option of extending your membership either with a credit card or by entering a "promo code", which is your token.
Once you enter the token, you will extend your membership by one year from the redemption date, so you will want to wait until you are close to your expiration date before redeeming in the token.
Note also that if you are in the United States, and have entered credit card information with WPDC, you will need to remove that information and disable any auto-renew options to ensure your credit card does not get charged.
If you are not currently a WPDC member, you may redeem your token any time. To do so, follow these steps:
1. From the "Token requests" tab on the Support screen, click on "Request" for the Windows Phone Dev Center token. 
2. You will see the token request screen. (We've hidden the token field here, but you'll see yours.)
3. Click on the "Windows Phone Dev Center" link and you will be taken to the Microsoft Dev Center sign-in/sign-up page. Sign in with your Microsoft account, or sign up if you don’t already have one. You will then be taken through the process of becoming a Dev Center member.
4. When you get to the step labeled "Purchase subscription", select the "I have a promo code" option, copy and paste your
Windows Phone Dev Center token into the promo code field, and click "Next" to finish the registration process.
