Use the Trim tool to remove parts of objects up to a boundary object. With…
Vectorworks Tip #033 – Basic Tools – Reshape Tool (Introduction)
This tool is so useful for reshaping parts of your design. You really have to learn how to use it. When you reshape a wall, polygon, polyline, callout, landscape area, hardscape, site modifier, etc. you use this tool. It has several modes and the modes are contextual, meaning that they change depending on the object you select.