Rooten Siding

Hi there everyone I have a problem in the Toilet area of my home, the weatherboards have become rotten before I owned the property and now this has rooted the upright studs and the floor plate. What is the easiest way to fix this, my plan was to remove the siding from the outside then cut the floor plate out and also the rooten part of the Stud and put a new floor plate in and bolt it to the concrete floor and put a new bit of wood in place of the old stud? Just wanting to know if this is the right thing to do?
Sory if the names of things are wrong am from New Zealand!