Resizing the figure is mentioned at Matlab's documentation.
Scroll down to the Change Figure Size section.
If you hadn't assigned a name for your figure, then use gcf (cf in gcf stands for current figure).
And put these two lines before your plot of interest.
If your aim is to just change the width and height of your figure as your question sounds like that, then you don't need to change the first and second entries of position. The first two entries are about the position of the figure window in your screen which you can drag and drop that window and has no effect on the size of the figure (and thus no effect on what you put into your paper/book ^_^).