Windows 10 upgrade is available for all the users who are using old versions of it from july 29, 2015. Upto now it is upto user that he want to upgrade it to Windows 10 or not when pop up message will come for upgrade authentication. But now scenario completely changed.
You can’t deny Windows 10 anymore. You just can schedule it later and after some particular time it will upgrade by itself only. when you will open system its upgrade will be processed. After one year for windows 10 upgrade we have to pay 10000/- , so its better to upgrade now only when it is free. Company is also trying to do the same but anyway it is taking user’s freedom. People who are using windows 7, windows 8 and windows 8.1 have to upgrade now.