[Zombies Aaargh]

I have a Lumia 640 which was shipped with Windows Phone 8.1, I upgraded it to Windows Phone 10.

I'm now looking at doing a complete wipe and restore on my handset to set it back to it's default settings with no data or apps on it. So I can start again from scratch.

Is there any way to reset it to a Vanilla version of Windows 10, or do I have to go back to Windows 8.1 and then upgrade to Windows 10?

If the latter, how should I best go about doing this?

[snikito]

I am not 100% sure but if you head to Settings-->About-->Reset phone it should reset to W10M. However I am not 100% sure so you better wait for someone else to confirm this.

[anon(10197358)]

@Zombies Aaargh

Do a hardware reset, this will not downgrade OS.

[Amarnath Subramani]

Use windows device recovery tool

[libra89]

Use windows device recovery tool

In this case, using the WDRT will take the OP back to 8.1.

[anon(10197358)]

@Amarnath Subramani

If you advise that, it's you don't know the functioning of Windows Device Recovery Tool (WDRT). OP want reset his device, but he prefers do it without rollback to Windows Phone 8.1. In that case, hardware reset is the only solution. For Lumia devices, WDRT download and install the latest package version avalaible from the Microsoft Azure repository servers, the package being determined by the CTR writed from the Device Provisioning Partition (DPP). And for non-native Windows 10 Mobile devices (like Lumia 640), the latest package versions contains Windows Phone 8.1.