1) Click the blue "Manage" button on the right side of the project page
2) Then select the "Change your pledge" Button.
3) Here you will be able to change your Pledge Amount by increaseing it to include your add on
4)After the campaign ends you will be invited to manage your pledge on our pledge manager, from there you will be able to select which add-ons you want
If you have any questions please send us a message or comment on the project page.