A redesign should begin with an inventory of the current pages, traffic, search performance, conversions and important inbound links. Removing or changing successful URLs without a plan can create avoidable ranking and user-experience problems.
What to consider
Map old URLs to the most relevant new destinations, keep strong content where it still serves customers and improve information architecture based on actual user needs. Avoid redirecting every old page to the homepage.
After launch, verify analytics, forms, sitemap, robots directives, canonical tags, redirects, mobile layouts and performance. Monitor search and conversion data closely during the transition.