unable to upgrade firmware T21

Hello,

I want to upgrade my current firmware to the latest version

My current:
Firmware Version 34.72.0.76
Hardware Version 34.1.0.0.0.0.0

Yealink Support Shows:

Firmware & Release Note
52.80.0.60

http://support.yealink.com/documentFront...umentId=77

I tried to upgrade manually but after waiting nothing happen. and a message show up on the phone screen:

update skipped!


what I have to do?