And when not to.
GOOD REASONS
The site does not work on phones It is genuinely slow and cannot be fixed The business has changed and the site describes something else It cannot do something you now need The platform is unmaintained or insecure
POOR REASONS
It looks dated to you, though it works A competitor redesigned theirs Someone suggested it You are bored of it
Visitors judge whether a site helps them, not whether it follows current fashion.
BEFORE REDESIGNING
Establish what is actually wrong. Frequently the problem is content or clarity, which a redesign will not fix and may make worse.
Check analytics: what pages do people visit, where do they leave?
THE RISK
Redesigns routinely lose search traffic through changed URLs and removed content.
WHAT TO PRESERVE
URLs, wherever possible Content on pages that rank Title tags, or improve them deliberately
THE CHEAPER ALTERNATIVE
Improve the content, fix the speed, and clarify the pages. Frequently that achieves what the redesign was meant to.