How do i remove tiles from maps?

I want to remove specific tiles from maps (for a game where you have to build and mine and stuff). How do i do this? (also i'm using Quickengine from @Gilles)

these are the map functions

map.get( x, y )	
map.set( x, y , "sprite" )	
map.set( x, y , "tilemap:4,6" )