How do I redirect old URL's to new ones?

If you want to redirect an old path to a new one "rewrite rules" need to be created in your stores .htaccess file. 

Say for example we want to redirect old.html to new.html first please locate;

RewriteEngine On

After this add:

RewriteRule old.html new.html [R=301,L]

This will make a permanent redirect from old.html to new.html. It's important to set the redirect to have a 301 header to tell search engines the redirect is permanent so they update their listings more quickly. The L flag tells the server to stop processing any other rules. You can add as many of these rules as you wish with one to a line.