Windows 10 is now available to some Lumia smartphones running on Windows Phone 8.1 Denim. Microsoft has recently announced.

The update for a limited number of old smartphone models began on March 17, which is about three months delayed from the company's original projected launch date in December last year.

The rollout this week, though, coincides with the statement they released in November 2015 as provided by ZDNet, saying: "This November we introduced Windows 10 to phones including brand new features such as Continuum and Universal Windows Apps with the introduction of the Lumia 950 and 950 XL. The Windows 10 Mobile upgrade will begin rolling out early next year to select existing Windows 8 and 8.1 phones."

The rollout of Windows 10 Mobile only includes select phones, which are the following: Lumia 1520, Lumia 930, Lumia 830, Lumia 735, Lumia 730, Lumia 640 XL, Lumia 640, Lumia 638 (1GB RAM), Lumia 636 (1GB RAM), Lumia 635 (1GB RAM), Lumia 540, Lumia 535, Lumia 532, Lumia 435, and Lumia 430.

As per the list, Windows 8.1 devices with less than 1 GB of RAM are not included in the upgrade. The company clarified that this is due to the significant innovations made for the new operating system. "Our goal is to only offer the Windows 10 upgrade to devices that we are confident can continue to deliver a good customer experience," Microsoft explains.

There are two ways consumers can get the upgrade. For those whose phones are included on the list mentioned above, they can download the Windows 10 Upgrade Advisor app, which is available for free in the Windows Store, and follow the steps provided to begin the upgrade.

Another way is to buy brand-new phones in which Windows 10 is already installed right out of the box. Consumers' options are the Lumia 550, Lumia 650, Lumia 950, or Lumia 950 XL.

The Windows 10 upgrade brings new apps and features into mobile devices. These include new alarm app, sticky keyboards, improved notification menu, and an all-new Office and Outlook Mail.