You are right this Samsung Model only supports 2.4 GHz Wifi frequencies according to GSMarena and Samsung phone specifications on samsung website as well.
It's not a simple as replacing a module. The firmware would need to be reprogrammed and re-coded for it to work including the phone kernel as well.
Even if this was feasible it would cost well more than the phone itself probably more than double the price to do.
The Wi-Fi chips on samsung phones are BGA mounted (ball grid array) meaning that they are soldered onto the board by being soldered on sitting on solder balls that are soldered onto circuit pads on the motherboard.
Not a easy thing to replace as it will require board level micro soldering and a lot of heat including a microscope.
TL-DR / Short Description answer: No not possible or feasible realistically.
I guess what we learn here is to always look at the phone specifications listed online via the manufacturer's website before buying the product if you are going to use certain features that most cheaper phones will not have.