The design mode within ActivInspire is part of the Professional edition of ActivInspire. You can check your current version by launching ActivInspire and clicking Help>About.
If you have your ActivInspire serial number to hand, this can be entered to upgrade to the Professional edition by going to Help>About>Register.
Please refer to article 10937 on http://www.prometheankb.com on how to generate an ActivInspire serial number using your Promethean hardware.
Support case 00519353