This administrator templates called blueplazza admin. And this totally different looks compares to joomla standard administrator templates.
This Blue Plazza admin has pastel blue header with "control Panel" logo,

Standard Joomla Back end templates

Blue Plazza Back End Templates
>> Download Blue Plazza Admin templates <<
How to Install this joomla administrator templates?
- Log in to your joomla administrator website.
Ex: http://yoursite.com/administrator
- Click Site -> Template Manager -> Administrator Templates
- Click New
- Browse your templates .zip files in you local computer
- Click Upload Files and Install
- Make it your default templates
refresh your back end pages, and it's done.