Safe that page as servers.def in \Program Files\Alwil Software\Avast4\setup
(that is if you have installed Avast in the default folder)

Overwrite the excisting servers.def

From the instructions thread:

Note that servers.def is a text file - so I recommend to right click the link and select "Save as". If you left click it, it may open in your browser as text (as a page). In that case, you can simply copy&paste it to the corresponding file, but the first method is definitely more convenient.