As reported last month, Windows 10 is likely to be finally released this summer and precisely July. If you click on this link, you can see what to expect but here’s what you would have to do when that day finally arrives but first please note that the software will be free for upgrade for Windows 7, 8, 8.1 and mobile users.
You would have update it from the “update” section in your control panel. This is likely to be a heavy download by the way so you would need to be a bit patient. This download will be P2P (peer to peer) and so if you require this update on multiple computers, you would need to access the pre-downloaded software from another PC which you can now install on other PCs