1. Open your map.
2. Browse to Extensions - Edit Tileset.
3. Click on the tiles you want to add, then click OK.
4. Don't do anything to the map, don't even save it. Close the map and open it again.
5. In Advanced - Modify Tileset, you can then change the order of your tiles. This is important to make the tiles overlap well. Tiles such as wines and leaves should be on the right and dirt on the left. But experiment with the tile order.
6. Enjoy your new tiles.