Windows 8 is now out in retail and if you are a legit Windows XP/Vista or 7 user you are entitled to a 39.99 USD upgrade. You can visit this link to download the Upgrade tool. Assuming you are still running the original Windows version your PC came pre-installed upgrade to Windows 8 will be straight forward. Apparently its even possible to upgrade if you have the Release Preview installed and a valid Windows XP/Vista/7 key (which is usually printed on a sticker on your laptop or desktop).
Unfortunately In my case I installed Windows 8 Enterprise Trial when RTM came out which is valid for 90 days (and has almost expired by now). That version cannot be directly upgraded and there’s no way on earth I will reinstall the bloated version of Windows 7 that came pre-installed on the laptop by Asus (I did create re-install media and probably have it somewhere but as i recall Asus tool filled 5 DVD’s). The only upgrade path I could take will involve re-installing the Release Preview and use my Windows 7 key; but I’d rather not lose the configuration and apps I have installed on the current installation which is after all final but just time-limited.
It seems you can still download the Release Preview ISO directly from Microsoft here for 64bit and here for 32bit. Now all its left is to find a way to trick it into downgrading Windows 8 Enterprise Trial RTM into Release Preview (which could possibly be done by changing cversion.ini)and then using the upgrade tool to purchase a Windows 8 license and upgrade to Windows 8 Pro retail.
I’ll run my experiments tonight after work and hopefully post a step by step guide if I get it done.