To remove a breakpoint under the cursor, click in the toolbar. Equivalently you can choose Debug > Stepper > Breakpoint .
Where you wish to remove one or more breakpoints without finding them in the source, choose Edit... from the Breakpoint Options menu or the menu command Debug > Stepper > Edit Breakpoints... , select a breakpoint or breakpoints in the Breakpoints list, and click Remove .
If you remove all breakpoints, then the breakpoints dialog is closed.
LispWorks IDE User Guide (Windows version) - 25 Nov 2011