The 'Change All Users Slug' plugin is built to help you to change all your user's slug in "/firstname-lastname/" (lowercase) format.
It is suggested to have a manually defined "Display Name" instead of having the same "Display Name" as the "Username".
If you want to use your username (login) for your user slug, then you don't need this plugin.
Just a standard installation required.
1.a Plugins > Add New > Upload > 'change-all-users-slug.zip' - Install Now
1.b Unzip & Upload 'change-all-users-slug' folder to the '/wp-content/plugins/' directory
- Activate the plugin through the 'Plugins' menu in WordPress
- Find the plugin in the 'Users' menu