To access your Default Connection settings, make sure you've clicked in the circle marked 'Connect to the Internet using a modem', in the 'Connection' section then click on the 'Settings' button.

From the 'Dialup Settings' panel, if you have multiple connections to the Internet you can choose which should be the default connection from the dropdown menu - where all your connections will be listed. If you intend to use Freeserve as your sole provider this should be set to Freeserve.