1) Login into HELM control panel.
2) Select the domain.
3) Click on icon Website Settings.
4) In the field Default Doc, add or delete the default content page. For Example : default.asp
5) To manage the priority, just reorder the entries accordingly. For example, you can write default.asp on first line to give it a first priority and you can write default.html on second line to give it second priority.
6) Click on save to change the settings.