WordPress URL Problems After Change it

You can do this with 301 redirects. There is a nice easy plugin that will allow you to do this.

https://wordpress.org/plugins/simple-301-redirects/

If you want to do it on a little lower level you can edit your .htaccess file with the structure you require. Yoast provides a easy to use generator available here:

https://yoast.com/wp-content/permalink-helper.php