- Go to cisco.com, search for your phone model and download the relevant firmware
- Copy firmware to a SFTP server (I run Solarwind’s free SFTP server on my laptop)
- Log into CUCM Pub: OS Administration–>Software Upgrade–>Install/Upgrade–>Remote Filesystem
- Go through the steps to connect to SFTP and upload the phone firmware
- Repeat steps 3 & 4 on your CUCM Subs
- On the Pub and Subs, log into Serviceability–>Tools–>Control Center – Feature Services
- Select the server you are logged into (Pub or Sub)
- Restart Cisco Tftp
On 10.5.2, the device defaults update automatically, and next time the phone reboots it will upgrade it’s firmware.