If you search youtube for something like "Frontier center console removal" or "Frontier head unit replacement" there are several videos there that will show you how it's done.
The top tray pops out, then you remove 3 screws, then the entire center console pops out. The HU is attached to the console by brackets on each side.
There is an extensive thread here titled something like "2014 head unit replacement, keep all oem functions" that is an excellent reference.