http://free.avg.com/us-en/faq.tpl-crp.num-2966
AVG automatically updates on a regular basis, making sure that your protection is always up-to-date. Although it is not necessary, you can also update your AVG program manually at any time.
There are several ways to update the AVG program manually:
Open the AVG program (double-click the AVG icon on your desktop or double-click the AVG icon in the system tray next to the clock).
It is also possible to update AVG by right-clicking the AVG icon in the system tray next to the clock and selecting the Update now option.