Its not a command. Hes suggesting that if all you're changing each map is the background image (thereby being the actual map) then the only thing you'd have to change is that, the background image. So perhaps having a variable called Map, and setting the Map variable to equal the level the user is on. Then loading the corresponding image for the Map variable. So, if your level 1 map is image 5, then you'd either start the Map variable out at 5 and load the image number of Map, or you'd start Map out at one and load the image number of Map + 5.
On the other hand if you're changing locations of dynamic moving characters, items that can be picked up, etc. Then you'd most likely want to go to a function. This route is up to you though, it really depends on whats going on the game, what will happen in the next level, etc. If you gave more info on what you need to load each level and what needs to be removed, more help could be provided.