Here's how to force update your Windows 10 if you reserved but still can't get the update

http://venturebeat.com/2015/07/28/how-to-f...0-update-files/

no you don't need to do that if everything is fine for you after upgrade.

the main reason i did that is to confirm that my computer has actually been registered with ms activation server already, and it can be activated online successfully without any key. another reason is just that i wanna create a plain activated system image, with all current windows updates applied, so that i don't need to go through it again and again when i restore the system.

clean install means the c drive where you install OS will be formated. so starting from scratch. Quick format is fine, as a full reformat i don't think is necessary 

can always resort to privazer for deleting traces if paranoid 

anyways got so many stuff installed in the old os, so you wouldn't want lingering unused files, to be on. so from a new clean install you got full control of what goes onto your new desktop :}

also saves time pruning irrelevant files from the previous os, apps installed (which you'll have to reinstall by the way using win10 versions of the app if available e.g. graphics driver...)