Old news for most probably, but thought I'd post this for those who have older models. I just upgraded my G55 from Win7 Home to Win10 Home, not that I wanted to, but...
Used the Microsoft upgrade website to download the upgrade tool, let it download 10 and let it roll with option to keep apps and files. Upgrade was painless, all apps and files are intact and work. I did, after the fact, upgrade the video driver from the Nvidea site.
As I figured from past experience, the touchpad lost all the smartgesture functions. Asus website says gen 7 and 8 Intel CPUs no longer use the Smartgesture software, which sounds valid as I could not install it once I wan on Win10. I tried 4 different versions and they all quit just short of final, with the same error message. Asus says the Elan driver is included in Win10 but I could not get that to kick in until I removed the touchpad in Device Manager, rebooted and upgraded the driver via DM. I had also updated the ATK software prior to trying to install the smartgesture file. Bad thing with the Elan driver is lack of functionality with the fnF9 key to disable/enable the pad. This can be done if you're using an external mouse via a checkbox in the Elan driver.
Oh, I also did not have to pay to upgrade, I was not asked to enter a code or validate anything as the upgrade accepted the Win7 license I had.