Upgrade SSD of my macbook pro (Retina, 15'', mid 2015)

Hi everyone, i'm an italian guy and i bought the previous mentioned mac with an SSD of 256Gb. In this period i need windows on my mac since some software that i have to use are only windows supported. So i thought to install it with Bootcamp but i don't wanna allocate a great part of my SSD resulting in a loss of performance of both the operating systems.

I wanna know if i have a solution to use windows in a stable and performed way, since my necessity is for collage studies, or how and if can i install a greater SSD.

Thanks in advance.