I've installed Update Advisor and it tells
Good news! Your phone is eligible for upgrade to Windows 10. We are working with your mobile operator and phone manufacturer to make the upgrade available for your phone and you'll see a notification when it's ready
But there is no update for a long time already, while my friend who has the same phone and mobile operator already got an update several months ago. I'm from Ukraine. How can I check if there's something wrong with my phone or force Windows 10 update by myself?