How to Change Structure of Permalinks?
You can change general permalinks from the ‘Settings > Permalinks’ page. That page has general WordPress permalink settings.
How to Change Structure of Post Type and Taxonomies?
If you want to change post type / taxonomy permalinks, you should use a plugin. If you change permalinks of post type from the codes of the theme, you can break the theme. The best way to change the permalinks are using a plugin. We recommend WordPress Permalink Manager Pro for this process. Also you can review or try free version of the plugin, click for lite (Free) version.