|You cannot. Just think of the chaos it would cause if such a thing were possible.|
Or do you mean install the Operating System over a Lan. Installing OS and formatting are two completely different things.
While it is possible to install an OS of a LAN, it needs specialised equipment and software. It would be quicker, simpler and cheaper just go out and buy a DVD or even a plain old CD.ROM which will be very cheap. Or alternatively temporary install the DVD drive in the computer you wish to install the OS.