If you are very eager to upgrade, tech savvy users with the above message can modify the following registry key to install immediately.
Locate the registry key: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\OSUpgrade]
It should exist, but if not, create it.
Create a new DWORD (32-bit) Value with Name = “AllowOSUpgrade” (without the quotes), and set the Value = 0x00000001.
Once the registry key is modified, close and reopen the desktop Control Panel, go to Windows Update and check for updates. You should now be able to click the Get Started button to upgrade to Windows 10.