You can modify configuration files (for example, edit the xml files) and add customized files (for example, custom ring tones, call back tones, phone backgrounds) to the TFTP directory. You can modify files and add customized files to the TFTP directory in Cisco Unified Communications Operating System Administration, from the TFTP Server File Upload window.
You can go with Personalization option and From Cisco Unified Communications Manager Administration, choose Device > Phone > Phone Configuration you can change it.