How to Install Windows 8.1 ( Fresh Installtion )
Install it
Browse ISO file
Click USB to make the USB bootable disk , DVD to make Bootable DVD disk
Then click on Begin copying , wait until it finish
How to Install Windows 8.1 ( Upgrade , those who have Windows 8 )
You can follow above steps , after that click on setup.exe on the USB drive. If you don't have a USB pendrive , simply mount that ISO file. You can see the Windows installation disk on the My Computer Window. Open that disk and click on the setup.exe file.