Best option to upgrade 7-speed bike to higher gears
Adding two or four teeth to the largest chainring will not improve you high gear very much.  Right now your highest ratio is 48/14=3.429.  Going to 52 will get you to 52/14=3.714, which is not much of an improvement.  It is better to focus on the rear, where 48/11=4.364  

Going to a new wheel set you need to check that the wheel is the proper width for the frame.  The space between the lugs might be 126,130, or 135 mm.