Map Help!

Im makeing a map called return of the dead and im almost done. but when i was gonna try it on on bnet it said file map to big. its 5.01mb but i see other maps that are rpg bigger then the one i made have a smaller file size like that worlf of warcraft reborn its huge. can anyone tell me how to make it smaller?

The rpgs must be single player, cus b.net cant handle 5 m+. To reduce file size, protect your map and delete some models.

Where Or How can i protect my map?