You can't upgrade internal storage - or at least, the risk of killing the phone if you tried is too great to be worth it.
I believe your phone does however have an SD card. A quick google will tell you the max size SD your phone supports but I'm guessing it will be at least 32GB.
You could install a file manager from the Play Store (I use a free one called File Manager) and use this to move things like photographs, videos and music from internal storage to the SD card.
If you need space in order to install the file manager, try:
- clearing app caches
- removing apps you no longer use
- removing updates for apps you don't use but can't remove
