The ability to manage your add-ons can be found under the service you wish to amend.
There are many options available, some with a charge and some are free of charge.
After you pick the ones you want you are taken to the next page to check what you have selected
Then onto the check out pages. Please note that all your products for that service will show, but you are only charged for those you have just added.
You will receive an email once the add-on is live on your account, usually within 24 hours.