You can force it.
Or create an usb stick for installation like I did.
http://www.microsoft.com/en-us/software-download/windows10
Yeah did this in the end. Only minor quirk was it wouldn't update unless I changed my region language from the UK to the US. But when it updated it installed it as the UK so all good.
Like it so far. Though it took a bit of playing around to get Cortana to work due to languages again. It will only work if you have your region language, speech language and language packs all the same and even then it takes a few goes to get it to actually start.
Like the overall look as well. More 'modern' looking than 7 and more streamlined over all. Edge is also nice and speedy so I've already switched from that to chrome.
The only thing that does annoy me is not having a 'My Computer' and 'Control Panel' in the start menu. I've changed that now by pinning them there though but the search wasn't originally working so was a pain in the arse to get to the control panel every time.