Can I upgrade my flash storage?

I just bought a 13" MacBook Pro with Retina Display about maybe 2 weeks, so I'm not exactly sure on what model that would be.

I purchased the most basic option, but totally underestimated the amount of storage I had. I was wondering if I could upgrade my flash storage from the 128GB (or whatever it is) to maybe something like 400-500GB.

Most of my storage belongs strictly to my music. I have 2 external hard drive (one from my 2011 MacBook Pro, and another) so I know I can just run my music from there to my iTunes to play music, but I feel it will be a nuisance if I want to bring my laptop anywhere, without my externals.

Just looking for some advice, thanks.