Deleting tiles is done using Blender's workflow for deleting faces.
- While in edit mode, change to face mesh select mode by pressing Ctrl+Tab
- Select the faces to delete by right clicking
- You can also use paint selection by pressing `C` and painting the selection. Scroll the mouse wheel up and down so change the brush size
- After selecting the faces/tiles you want to delete, press `X` or the delete key and select `Faces`