To remove a breakpoint under the cursor, click 
in the toolbar. Equivalently you can choose
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 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 (Unix version) - 25 Nov 2011