On the home tab - left side is the zoom feature. The default is 100%. I usually use 200% when I'm adding stitches and often go to 400% if I have to do a lot of quarter-stitches (it's easier to point to the appropriate areas.
One other point - the size of the stitches, even with the zoom factor depends on the count of the pattern you are creating. 200% at 14 count results in bigger squares than 200% for an 18 count pattern.