Well, you run the Windows Upgrade Assistant from http://windows.microsoft.com/en-US/windows-8/upgrade-to-windows-8 (or the one from your local Microsoft if you don't want the USA version) and it all goes automatically (after you paid for the download).
You can't go back to Windows 7 unless you made an image of your disk (at least the partition that has Windows on it, and the BCD also).
Hello This is joelmasan. Presently My system OS is windows7. I want windows latest version 8 on my pc.
I dont know how to upgrade windows7 to windows8. so, any one over here please suggest me the process of upgradation. thank u in advance.