Login to your control panel at http://control.apexhost.net.au
Please note: Ensure you set your site to Dedicated Application Pool before changing the dotnet version.
Application pool is set under Web > Websites > Click on your domain URL > Home Folder tab, click on Dedicated application pool tickbox
Once logged in hover over the Web Icon then select Web Sites
Click on your domain name link
Click on the Extensions tab
Select the version of dot net in the drop down list. 1.1 for version 1 and 2.0 for 2.0 and 4 for 4.0. and above
Click on the update button.