Following an initial release that the new windows 10 OS will be released early this year to devices already running windows 8.1 questions have been going about which devices gets the update or not. In other to stop the whole confusion, Microsoft has developed an app(still in its beta stage) that can let you determine if your windows device is upgradable to the latest OS or not dubbed Upgrade Advisor. The app which is now available in the windows store lets you know if your windows 8.1 mobile phone is eligible for an upgrade to windows 10 and can also help to free up space on the device so you’re ready for the upgrade.
There are a few requirements your present device must have to expect/accomplish this update; First of all you’ll need at least 8GB of storage of which 1.5GB is the minimum for the installation process to work and your current Lumia device software version must be running on the Lumia denim update i.e 8.10.14219.341 or higher
In the meantime, official announced list for Lumia smartphones eligible for the free upgrade when available are as follows Lumia 430, Lumia 435, Lumia 532, Lumia 535, Lumia 540, Lumia 635 (1 GB RAM), Lumia 640, Lumia 640XL, Lumia 735, Lumia 830 & Lumia 930. Features may vary by device.