..is it possible to change the IP address using UART?
Yes and No!
Yes is is possible to do, but not on a new or factory reset module.
You have to log in on the network side using telnet in order to enable RCI serial.
set rciserial state=on
I think you can also activate it through the web interface, but I find the telnet method quicker and easier.
Once done, you can then use RCI mode at any time by activating the DTR pin (i think?) where you have access to all of the module's settings. Unfortunately, the command language is XML, so if you are using a small microprocessor, the task is not trivial.