Log into your membership at EricChurch.com, click on the "Discount Codes" tab, click on the code and you'll be directed to the store so you can select your music. Your code will be automatically applied to your order.
If you have already used your discount code, you may not be assigned a new one. New codes are assigned at renewal or upon signing up/upgrading. You may not renew early in order to get a new code.