When a passport is renewed, the old passport is canceled, and a new passport with a new number and expiration date is issued. The new passport might come with new information added to it, such as new visa information or a new photo, but it is not considered to be a "new" passport in the sense of starting over with an empty document.
As long as the current passport is in good condition and has not been damaged, it can be renewed multiple times before needing to be replaced with a new passport.