If the download was zipped, make sure it gets unzipped. You'll end up with a folder, that itself contains subfolders named "data" and "region" and a file named "level.dat" among others.
That folder is the safe file. (the whole folder, not the individual files)
Now, find the instance folder for your install of FTB lite, and inside that find the "saves" folder. Then move or copy the safe file you've downloaded to that folder.
If you've done this correctly the map should appear in the list of saved games inside the game.
