Unable to update firmware from 2.5.4

Dear Colleagues,

VS-GWM400.
Hardware Version: Date 2012-11-09 FPGA 11 Hardware 00

I have strange case - on main module I have 2.5.4
and on slave I have 2.5.0

And I can't update via UI.

Connecting via cloud - cloud.openvox.cn

Auto online upgrade fails. Upgrade via UI using www.openvox.cn/pub/firmwares/GSM%20Gatew...ases/wg400-2.5.8.bin also fails:
----
System Updating ......
Slave: 192.168.12.110 System Updating .....
Slave: 192.168.12.110 Update 192.168.12.110 failed(couldn't connect to host)
System Update Failed
Retry angain.
Update 192.168.12.110 failed(couldn't connect to host)
System Update Failed
Retry angain.
Update 192.168.12.110 failed(couldn't connect to host)
System Update Failed
Please manual re-update!!!
----

Please assist.
How to upgrade ? Is it possible if I have ssh access to GSM gateway ?

Hello，

Yes, you can update the slave board firmware via ssh , Please give us your skype here , we will add you , and then you can prepare teamviewer for remote checking .

Thank you a lot for fast reply.
Added you to Skype

Hello

Give us your Skype ID please .

sure:
onanchenko.sergey

issue was solved.
many thanks to Vito Rao and Dario Hu.

upgraded firmware on slave first from 2.5.0 to 2.5.4 and then to 2.5.8.
did so via ssh - firstly uploaded firmware to /data via scp (please note that slave has different port for ssh - 12346 in my case)
and then

cd /data
/my_tools/unpack.sh wg400-2.5.8.bin

then reboot.

Thank you for assistance.