How to download and install the Windows Phone 8.1 update
How to Install Windows Phone 8.1 Developer Preview - YouTube Apr 15, 2014 How to Install Android Apps on Windows Phone (Windows 10 May 08, 2020
Microsoft will shutdown Windows Phone 8.1 Store in December
How to Install Windows Phone 8.1 Apps and Games Manually
Eligible devices: 1. Lumia 630, Lumia 635, Lumia 636, Lumia 638, Lumia 730, Lumia 830. 2. To install windows 10 for phone, the device should be running with Windows 8.1 in it.
If you want to update old Windows Phone 8 firmware version to the latest Windows Phone 8.1 Preview firmware version, then your device warranty will be voided until you download and install the official final public release of Windows Phone 8.1 Update and also once you updated to Windows Phone 8.1 then you won't be able to revert back to the previous Windows Phone 8 or earlier version.