If the update doesn't work, or you don't have an automatic update feature, you will have to go to the website of the manufacturer to find the latest updates. Find the latest update for the operating system that you are using and download it to your computer. After you download the update, you must install it by finding the file and double-clicking on it. An important thing to note here is that the virus update files can be very large. If your memory cache is set too low, you will get through only a part of the download.
Most people then retry the download again and the same thing happens again.
Three or four frustrating hours later the download still has not completed. There is an easy fix for this. If you are using Internet Explorer, on the Tools menu click on Internet Options. Then on the General tab, click on Settings. Move the slider to the right to create a larger cache.