We can but try …

Download the correct version of Avast
Avast Free
Avast Pro
Avast Internet Security
Avast Premier

Select Custom install
Remove the ticks from the first page for the following unless you want them :

https://dl.dropboxusercontent.com/u/73555776/avastchrome.JPG

Dropbox
Chrome
Chrome toolbar

Select Next
Deselect the following from the middle column as you will not need them :

https://dl.dropboxusercontent.com/u/73555776/avasttools.JPG

SecureLine
Grimefighter

Select Continue and allow the programme to install

Be aware that the first reboot may take a few minutes as Avast builds the virtual machine

Avast will need to be registered as this helps them determine the server load, as updates are downloaded in small bursts every few minutes each is about 2Kb

How to register

Right click the Avast orange blob on the task bar
Select registration
Select Standard Protection

https://dl.dropboxusercontent.com/u/73555776/avast%20register1.JPG

Fill in your e-mail address

https://dl.dropboxusercontent.com/u/73555776/avast%20register2.JPG

Click register with e-mail address and you are done
Once registered open Avast
Go to Settings > General
Place a tick in "Scan for Potentially Unwanted Programmes (PUP’s) "
Place a tick in “Silent /Gaming mode”

https://dl.dropboxusercontent.com/u/73555776//pups.JPG