I have a ZTE phone with an internal storage totalling 16 gb. But my system memory (that I can't access / alter) is taking up 8.09 gb. I need that space for other apps, what can I do?
Welcome to Android Central! The OS and preinstalled apps will always take up some space. Some phones with a lot of bloatware can use up that much space. The only way to get rid of bloatware would be to root the phone.
About all you can do as a reliable solution is replace the phone with one with more internal storage. At minimum, 64 GB plus an SD card (for independent files), or 128 GB without an SD card.