You do not right click, you click on the avast icon on DESKTOP or right click the one in taskbar, if you right click on taskbar icon click Start avast! antivirus then a screen should pop-up saying avast! 4.8 home click stop memory test. Now that avast! had loaded click on the icon in TOP LEFT CORNER OF WINDOW. One of the options will be Schedule Boot time scan.
This will scam your computer nextime you reboot (before windows has loaded). Press esc to skip the scan when the screen comes at boot-up.