Removing map elements varies slightly depending on whether you are removing boundaries or features (elements you place on your map that are inside your boundaries).

This video details how to place, modify and delete property boundaries (scrub forward to around 1:55 for specifics about deleting a boundary):

http://mylandplan.org/video/how-add-property

This video details how to place and modify features and points of interest.

http://mylandplan.org/video/add-features-and-points-interest