The number of undo steps available in OpenOffice Calc can be changed using the Options menu. To change the number of undo steps, click Tools menu and select Options from the list of menus. This would display the following OpenOffice.org Options window
Under the OpenOffice.org tree, click the Memory node which would display the following Options Memory window.
You can increase or decrease the number of undo steps using the Number of steps available as part of the Undo section.