If you are hoping to find a magic file that converts your existing ZTE MF65 into a 4G LTE device, the short answer is: .
Fixes frequent disconnections from the 3G tower.
Wrong APN settings cripple speed. For free, you can:
If you want to keep using your current device or switch to a new one, let me know: Which are you currently using? Is your 3G network still active in your local area? Share public link
Unlocking allows you to use faster HSPA+ SIM cards from other providers, which is the closest "free" performance boost you can get. ZTE MF65 Manuals - WorldSIM
While you cannot upgrade the device to 4G, you can upgrade its utility for free or a very low cost by . Unlocking allows your ZTE MF65 to accept a SIM card from any network carrier rather than being tied to the provider you bought it from.