1) Install Lumia Help + Tips from store, if you don’t already have it on your device. Here is the link
2) When you open the Lumia Help + Tips on your phone, you will see the option of “check your warranty”
3) Tapping on “check your warranty” not only shows the warranty status of your device, but you can also extend warranty, if the option is offered in your market.
For similar Windows Phone tips and tutorials, check our “Tips & Tutorials” category.