if there is enough memeory in your gps, then just

copy that gmapsupp.imp into gps, turn on gps and go to "map info" menu, there will be two maps, you can just select one you like; if there is not enough memory in your gps, make a backup gmapgrom.imp on your PC, then delete gmapgrom.tmp from gps, and copy gmapsupp.imp into gps, no need to rename gmapsupp.imp.