You can set the Position property of the axes if you want to keep the figure the same size. If you want to enlarge the figure as well, set it's Position property (after which you might also need to set the axes Position.)
Note: if you use subplot() then if the new subplot would overlap any existing axes, including another subplot, then axes that would be overlapped will be deleted. However, if you set the subplot axes Position properties after you have finished calling subplot() then you are fine.
