Instructions
Click on the "Hammer" icon on the tool bar at the bottom-left side of the screen. Select "Floors" from the next menu of options. The icon looks like a small piece of floor tile.
Select the type of tile that you'd like to use, and then click and hold the left mouse button to drag it. Drag the tile to where you'd like to place it on the floor, and then release the left mouse button.
Drag and drop enough tiles to cover up the previous flooring. The new tiles will cover the older ones.