Can return my new macbook and get a better one? (paying for the difference)

I have just bought a Macbook Pro (4 days ago) (mid-2012) non retina 13". I am so disappointed with the booting and speed of my macbook and also I have some lags and delays. One of my friends told me that your macbook is an old version and there is no actual problem with it! I wonder I can return it and change it with better one (for example Macbook pro retina 13") and pay the difference?

It is noteworthy that I bought my macbook through university portal and got some discount. Can I get discount for new one as well?

Thanks!