Flashed up Samsung C5 but my Internal memory is now 16 Gb droped down from 32 Gb ?

Hi , I just Flashed up my Rom but I now find my internal memory only 16 GB ?
I am using a Samsung Galaxy C5 ! Can anyone Guide how can I just Upgrade it or do anything to restore it to 32 GB as the Phone is 32 Gb from the Company ?
Thank you