For Redesigning a website you should know about the following but the first Audit you Website
1. Why you are going to redesign
2. Who are your Users
3. What is the theme of the Website
4. Choose web design wisely
5. Content should be unique and fresh
6. Update content that your users want
7. Color Scheme
8. Font Style matters too
9. Don't forget to correct the mistakes in a new website that you did in Old website

You can read more about here Website Redesigning Tips