Wordpress has already built in features that will assist you changing the website to friendly URL. I suppose that you are not only concern with the way to create friendly URL but also with the SEO impact in rankings or traffic that this might have. Read this answer here about 301s.
1) create a database backup. In case you make a mistake you will be able to rollback your changes. There are many plugins available to help you with this task if you don’t know how to do it yourself via cPanel.
2) You can start by changing the way your CMS shows the URLs. Go to settings menu, select permalinks and choose “Post name”. This will automatically change the urls to the main title of your page/posts and create the 301s for you. You can always comeback here to change the URLs to a more advance structure.
3) If you would like to change the URL structure, assign new categories, etc export your Urls following this instructions here. Then, apply
this procedure to make life easier for you.
4) make sure your new urls follows a comprehensive website structure, using categories and subfolders correctly, and reflecting that in all your navigation menus.
5) update all text based internal links within the content of your pages to point to the new URLs
6) update your sitemap, for this use a plugin like Yoast SEO. Make sure to re-generate your sitemap and re-submit to google and bing search Console.