The company uses a Zyxel EX5501 (as labeled), but it's running Arris firmware (likely a dreadful carrier-customized version), which is extremely difficult to use. It doesn’t allow changing the WiFi name or password, only functions as an AP, can’t assign IP addresses, and the backend is very hard to access—I had to search through a ton of resources online just to get in. Worst of all, the upgrade page only allows firmware uploads smaller than 8MB. This isn’t a half-finished product; it’s junk. How can I flash it back to the original Zyxel firmware?