One method to try, go to Windows Update i.e. Windows Start>All Programs>Windows Update
In there you should see the Windows 10 Installation listed in the 'Optional updates' list. If so, untick the box then Right-click the text and select "Hide update".
If you can only see "Upgrade to Windows 10" listed and don't see any other potentially available updates, click the option 'Show all available updates' located beneath the 'Get Started' pane, then check the Optional Updates list.
Restart your system and check if Win 10 Installation is no longer showing in the optional updates list. If necessary repeat the process.