Yes, it is possible to replace wireless card in this laptop. You can purchase a new one [http://www.laptopinventory.com/ModelDetail.php/Toshiba/Satellite/S55t-A5389/Wifi%20Card/41953|here].
As for a replacement guide, there is not yet one available for this laptop and I am not able to create one as I don't own this laptop. I recommend searching Google if you haven't already.