The changes from LTE to 5G/new radio on the RAN part are small actually. The step from LTE system architecture to 5G service-based-architecture in the core network function was quite big and enabling a lot of X-as-a-services (read as: move to cloud). Technically you can run a 4G/5G network with a little bit of smallcell RAN and a single VM running your core (read as: i did in a lab scenario).