Hello! My name is Mustafa, and I am an Independent Advisor as well as a long-time Microsoft user. I am hopeful that I will be able to help you find a satisfactory solution.
Unfortunately, this is not possible, the device supports 3g, and to have a 4g on a device, the device should come with the hardware equipment required for a 4g. So a software update is not going to get you to 4g.
Please let me know if this doesn't work or if you need further assistance.
Warm Regards,
Mustafa