https://www.raspberrypi.org/downloads/raspbian/
1- determine the raspberry pi type ( 1,2,3,4)
2- download the correct img
3- format the SD card ( gparted)
4- install the img file (win32 Disk Imager )
Can use the Installer from Xbian which will download the latest RPi version
With Win32 Disk Imager: unzip,untar the file and select the .img file