how to upgrade 8088 phone

[Timmie]

on my company we have a problem with 2 8088 phones.
1 of the 2 phones is an older software version R100.1.008.2 and we need to upgrade it to the newest firmware.
the problem is, we have no idea how to upgrade them.

can you update them just through USB ?
or does the phone first need to be connected to the oxe?
we have no idea at all.

if anyone knows the steps to upgrade these phones, this would be a great help.