Going from one template to the other is simply unbinding the network from template 1 and then binding it to template 2. This can be done under Organization->Configuration templates and selecting the template to unbind and then bind.
The actual changing of templates is pretty straightforward, but how seemless this will be for end users depends on how each template is configured, as well as the network upstream of the APs. If everything is in place, vlans, DHCP servers, etc. it should be pretty smooth. This can all be looked at and planned ahead of time to minimize any impact during the actual switchover.