Yes if you have your PBX loaded with operational software on it.
You can use the GUI and HTTP protocol or TFTP protocol to make software update.

As a first step put the uImage-xxx-md5 file so it is http visible. (alternatively tftp visible)  

In the PBX GUI go to 'Firmware upgrade' (in the advanced options section) and select HTTP URL. You can reset or keep the PBX configurations using the provided check box.
You need to specify the full path and file name for upgrade including 'http://'.

If you prefer you can update uImage using TFTP protocol instead of HTTP. In this case please specify the IP/host_name of your TFTP server.
You need to specify the uImage file name as well.

The actual software update will happen on the next reboot of the PBX.