You already have an IMG-file in the correct format (e.g. Garmin propriety IMG map container format, not a disc image that some believes).
HomePort reads the file from a connected Garmin unit, memory card or a USB-stick. Just copy the file as "[USB mass storage device]:\Garmin\gmapsupp.img".
The same goes for your Garmin GPSMAP 440s, just copy as "[SD card]:\Garmin\gmapsupp.img" and put the SD card in the unit.
Here I have HomePort with a microSDHC card as drive "L:" and the map stored at "L:\Garmin\gmapsupp.img":