This report addresses the user query regarding the possibility of upgrading a portable Wi-Fi router from 3G to 4G (LTE) standards. Numerous online searches and "free upgrade" claims have been investigated.

ZTE MF920N 4G Mobile WiFi | Unboxing and Spec Breakdown - YouTube. This content isn't available.

Enable this for free (though it uses your phone’s battery). For extended use, keep the phone plugged in.

Some cellular carriers use the term "upgrade" to mean changing your SIM card or data plan to include 4G access. A user might receive a free SIM swap from their carrier, insert it into their MF65, and see no change. The device continues to connect via 3G because the hardware dictates the protocol. The "upgrade" applied to the account, not the device.