Making a website accessible without starting over
Here is a straightforward look at this topic for Crazish.
Accessibility is often treated as a large project, yet most improvements are small and can be made page by page. Start with the basics: enough contrast between text and background, descriptive link text instead of vague phrases, labels on every form field and captions on videos. Each fix helps people with disabilities and usually makes the site easier for everyone.
Test with the tools you already have. Try moving through a page using only the keyboard, zoom the browser to two hundred percent and check that nothing overlaps, and switch on the screen reader built into your phone for a few minutes. Keep a short list of problems found and fix the most visited pages first, then make the checks part of every new release.