Options - Edit
On the Tools menu, click Options, and then click the Edit tab.
Select this check box and enter a value to place a limit on the number of steps of Undo/ Redo information FontCreator stores per font. The range is from 1 to 999999 steps per open font.
Max. size [KB]
Select this check box and enter the amount of disk space for FontCreator to use when storing the Undo/ Redo information. The value can be between 1 and 999999 KB of storage per open font.