Hopefully Lift File Manager uses Twitter Bootstrap Framework meaning that you can easily change its skin to your favorite skin based on your specific project.
So follow the below steps to do so:
1- Choose your favorite skin from Codecanyon ( Recommended ).
2- Upload the new skin next to the default bootstrap stylesheet used in Lift File Manager on your server
3- Now open the file header.php with a simple text editor or whatever you better prefer and add your favorite skin after this line:
NOTE: You can find header.php in ../filemanager_admin ( This is for the Admin Panel ) and ../filemanager_user ( This is for the User Panel )
NOTE: You can find a file named login.php in both of the above directories and apply the same changes if you want to change the login page style for both of the admin and user login pages.
NOTE: Bootstrap 3 Skins recommended.