My advice: brew your kit exactly according to the directions. You'll have a mush easier time coolling those 2 gallons than you would a larger boil, and your recipe is formulated for a 2 galllon boil.
Here's why it matters in recipe formulation: the higher the specific gravity (concentration of sugars in the wort), the lower the efficiency of extraction of bittering compounds from the hops.
So, a larger boil means a lower gravity wort, which means you'll extract more bittering compounds from the same amount ot hops.
You can use the free Beer Recipator software to play with these numbers
http://hbd.org/cgi-bin/recipator/recipator
But any improvement you could make in your kit's quality would be negligable. Just brew it according to the directions and concentrate on getting comfortable with the process.