Please take care: when WordPress users are deleted, any content they have authored must be reassigned to another WordPress user, otherwise the content will be permanently deleted.
If you have the Super Admin role, you should be able to delete users from your site yourself, via the user list at the Network level:
- Go to the user list: [your site]/wp-admin/network/users
- Underneath the user’s name, select ‘Delete’
- If the user is an author of any content, you will be asked to attribute their content to another user. Select ‘Attribute all content to’ and choose another user to be named as the author for that content.
- Click ‘Confirm Deletion’.