the nano should have come with a full guide in the box m8
download an image, then unzip the image onto a usb stick, so when you look at the usb stick in 'My Computer' you have a single folder called update. open this folder, and theres a folder called tmnonooe, and open the folder inside that called 'cfe' in here you will have a few files, if one of them is called cfe.bin, delete that file, but leave the others there, if this file does not exist, then youre all good
put the usb stick into the receiver, turn the power off and pack on at the little switch on the back, and itll tell you on the screen that new firmware is found, and tell you to pres OK on the receiver, press this, and itll update and inform you when its complete