if you downloaded an unlocked IMG ,yes you must rename it gmapprom.img
if you downloaded a locked one you must unlock it with jetmouse keygen
[Only registered and activated users can see links. ]
create a notepad file names gmapprom.unl (no txt ext,save as all files in notepad)
if you have more than a map in your unit rename it gmapprom1.img
if you want to put it in an mmc ,rename it gmapsupp.img and create a gmapsupp.unl and put both in a named Garmin folder in mmc