What is the best way to backup my sites?

I want to backup my two sites before upgrading to 3.9.2 but have never done this yet. Can anyone suggest the best and easiest way to do this? Should I use a plugin? And I’m not the most well-versed with WordPress and software, nor am I a programmer but I do have some knowledge of WordPress (I recently used the Image Widget to add a link to my sites.) Any help will be greatly appreciated, thanks.