What plan are you to changing to? Have you purchased a new HD television?
It depends on what equipment you now are using.
Thnkas for reaching out. The information provided by @MNtundraRET is correct. Depending on your plan and the type of television you have, you may or may not need to upgrade the box. If you'd like, I can review your current plan and equipment to confirm whether or not you will need to swap the boxes.
Just send me a message by clicking on my name, "ComcastChe" then click send a message. In the body of this message please verify your first and last name.