Changing Object's Shape
Cut an Object with the Knife Tool
The Knife tool can cut paths and objects into parts. This tool also works with groups and compound groups.
To activate the Knife tool, click on the Knife icon in the Tools panel.
To cut an object or path, select it. Then draw a cut line over that object or path.
To have a straight cut, press the Opt key before drawing a cut line. In order to snap the cut line to 45, 90 degrees and so on, hold down the Opt and Shift keys.
If you cut a closed path, paths of created objects will also be closed. The program will automatically add new path segments where they are needed.