Sabayon-Linux doesn't really have a "Set-It and Forget-It" type of automatic update.
They are making progress at simplifying the update process, but at this time, you are probably best off with learning how to use emerge to update. You can use a graphical tool like portato, or use the command line method laid out by Wolfden in this Wiki entry:
An alternative way I've seen several people mention is to just wait for the next DVD release, and use the installer upgrade option.
Myself, I use Wolfden's method.