To remove cells in a ClarisWorks spreadsheet, simply choose Document... in the Format menu, and type the appropriate number of columns across and/or rows down before clicking OK.
Should this action result in an error message "The selected value must be in the range x to x", it is because ClarisWorks thinks there is data in one or more of the cells you are attempting to remove. Sometimes this is an invisible formatting character which can't be seen on screen.
To resolve the problem, drag-select through the cells you are attempting to remove and choose Clear in the Edit menu.