save as new map besides it is always good to have atleast two of everymap that is important to you. Halo Reach has issues with map saves sometimes and will replace your map with another, without changing the name sometimes. It sucks, I've lost only 1 to this so far, but thats because I learned my lesson quick.
The only way to rename a map in your File Share is to completely replace the map, uploading a separate file. Naturally, the two files will have different download/Like/recommend counts, etc.. While Forge is excellent for making maps, the file sharing systems that have been built around it are dreadful -- it's impossible to view File Sets in-game, making file grouping near-useless; one can't view Like/Download/Recommend counts in-game, so it's hard to know if a file is worth it; aside from totally replacing a file and resetting all counts, there is no facility for updating one's maps/gametypes...