If you would like to upgrade your existing SingleFeed plan to a different plan you will need to visit the Profile page of your account. You should see the text "Service Plan" and right below it will be a text link with the name of your current service plan. Click on this link and a new window will appear and list all the plans that are available for you to upgrade to. Select your new service plan and then click "Save Changes". You will be notified of the new plan price and if any credits or debits will be applied as a proration from your current plan.
If you have any questions at all, or if you have any issues upgrading your service plan, please let us know by filing a support ticket. Or, if you have a Premium account, contact your account manager directly.