If you find your computer has become infected follow this guide to get it cleaned up.
Links to the relevant tutorials have been included to simplify things for you.

Step 1
Run ATF-Cleaner
This will quickly clean up some items.

Step 2
Run CCleaner - Cleaner Section

Step 3
Run CCleaner - Registry Section
The above 2 steps will more thoroughly clean up the computer.

Step 4
Run AdwCleaner
This will hopefully get rid of most infections quickly.

Step 5
Update Malwarebytes Anti-Malware
Run a scan with Malwarebytes Anti-Malware

Step 6
Update SUPERAntiSpyware
Run a scan with SUPERAntiSpyware

Step 7
Update Avast
Run a scan with Avast
The above 3 steps will possibly find infections that are being missed by each other.

Step 8
If infections were found then carry out steps 2 to 7 again, this will ensure remnants are cleaned as things do get left behind and also sometimes it will take a couple of runs with scans before everything is removed.

If you find infections keep reappearing after a few scans with all of the above then it's time to visit a site that has a section that is dedicated to removing infections.

If you get to the stage where the computer is coming up clean, which hopefully you will, then proceed as below.

Step 9
Run the Avast Software Updater
This will quickly update some programs.

Step 10
Run the FileHippo App Manager
This will make sure everything else on the computer is up to date but requires a more user interactive approach than the Avast Software Updater.

Step 11
Update SpywareBlaster
This will add an extra layer of security to hopefully keep it infection free in the future.

Step 12
Manually Check for Windows Updates
An updated computer is less likely to get infected than an outdated computer. Hopefully your computer is updating automatically, or at least will be notifying you that updates are available and you are keeping on top of that, but checking for updates manually after a clean up won't do any harm.

Step 13
Restart the computer (if there were updates available and you installed them and you wasn't told to restart while carrying out step 12.

Step 14
Run CCleaner - Cleaner Section again

Step 15
Run CCleaner - Registry Section again

Step 16
Run MyDefrag

This should result in a much smoother running computer but will take up quite a bit of your time. Run the scans when you have other things you can go off and do maybe.