The biggest risk when redesigning is losing in a night the search rankings you built over years. The cause is usually not the design but changed addresses with no redirects.
Step by step
- List the old URLs. From the sitemap, Search Console and server logs, extract the addresses Google knows and visitors use.
- Map them. For each old URL pick the closest new page. If none exists, redirect to the relevant parent category.
- Set up 301 redirects. A permanent redirect carries most of the ranking value to the new address. See the 301 redirects guide.
- Avoid chains. Old → new should be a single step.
- Keep titles and descriptions. Do not carelessly change the title and main keywords of pages that rank well.
- Monitor after launch. Check crawl errors and 404s in Search Console daily in the first weeks.
A real example
The old version of this site used date-based URLs (/2019/08/31/post-name/) and old pages were still being requested. In the new version we linked all of them to new addresses with 301s; it is a standard part of our SEO service.
If you are planning a redesign, see our web design page, and read the process together with 10 things to check before building a website.