Step 1
Open your website folder in your preferred editor.
We would recommend Visual Studio Code.
Step 2
Find and replace the file ~/wwwroot/css/uSkinned/icons/icons.css with your own icons file.
Step 3
Login to the CMS.
Step 4
Update the 'Class name regex' field within icon datatypes to your own icon prefix: Settings > Data Types > USN Data Types > Link Picker.