If you select Custom update, you will see the component selection dialog.
Any line in the components list that starts with a plus sign is a grouping of components. You can see the listing of these components by clicking on the plus sign. A red checkmark is a component that our engineers have determined must be updated for Outpost Firewall to avoid compatibility problems between modules and other selected components.
Check the components you want to update. De-select the components you do not want to update. It is recommended to update all components unless you are an advanced user and have some reason not to.