WARNING: Deleting users is not recommended because the data and user cannot be recovered. Please be careful before using this feature.
1. Use the admin menu to navigate to Users > All Users.
2. Search for the desired user you need to change and click their corresponding link.
3. The next page that loads is the edit user page, click the delete button.
Alternatively, a more recommended option would be to use the edit user page to click on the Permissions tab, uncheck 'Is Active' checkbox and then save. This would deactivate their account rather than delete it.