This tutorial gives you the exact steps you need to do to download Windows 10 directly from Microsoft via Windows Update.
Microsoft has stated Windows 10 will be sent out to American customers first and international users second. Windows 7 or 8 tablet users will be last. You could wait anywhere between a few days and 3 months for the update to be sent out.
This tutorial outlines everything you need to do to force Microsoft to send you the next available download of Windows 10!