So, today, Mavericks (GM) came out, so we'll be upgrading from 10.8.3 to 10.9
It is pretty similar to upgrading from Lion to Mountain Lion.
Install Chameleon.* A couple options are set by default, so, make sure you do a 'Custom' installation and uncheck anything that says 'Lion Only', and uncheck GraphicsEnabler=Yes
*Backup your current Chameleon installation: i.e. in your root directory '/', the file 'boot' and folder 'Extra'
Create a bootable USB drive with MyHack.
- Open MyHack
- Choose 'Create OS X Installer', then 'Create OS X 10.9 Install Disk'
- Restart your computer and boot the USB drive. It will launch the 10.9 Installer
- Chose your current Mountain Lion installation when it asks you where you wish to install. (it'll say something about your current installation being recoverable)
You've now installed Mavericks!