To delete a single seat from your seating chart, left click on it to make it turn green. In the image below, I have selected seat A5.
While still hovering over the seat, right click on it. The option to delete the seat will appear.
Delete a Row
Right Click on the Row Letter to delete a whole row.
Do Not click to individual seats to delete an entire row, this will cause you to have an error in the processing of the section.