While looking at the campaign page, at the top you should see a green (or sometimes blue) button in the top right corner the says Manage Your Pledge. Click on that button and it will take you to a page to where you can change your pledge. Click on the blue (or possibly green) Change your pledge button. On this new page all you need to do is adjust the dollar value in the box. If you want one of the Add-Ons, you can increase your pledge amount by $7. If you want both Add-Ons, just increase your pledge by $14. Everything else will be sorted out in the BackerKit pledge manager.