How to edit existing Xml using Iron Python?

I'm trying to edit an existing xml using Iron python but nothing works.

My Xml contains some data regarding the screens connected to my computer, and I want to change the resolution every time . Example :

<monitor id="16843008" adapterHigh="0" adapterLow="31682">
    <name>IBM L190p</name>
    <!--source: the origin of the video signal-->
    <source id="0">
        <name>\\.\DISPLAY1</name>
        <path>\\?\PCI#VEN_8086&amp;DEV_0126&amp;SUBSYS_21CE17AA&amp;REV_09#3&amp;e89b380&amp;0&amp;10#{5b45201d-f2f2-4f3b-85bb-30ff1f953599}</path>
    </source>
    <size width="1280" height="1024"/>
    <position left="1280" top="0"/>
    <!--8bpp-->
    <!--16bpp-->
    <!--24bpp-->
    <!--32bpp-->
    <!--Non-GDI-->
    <color value="32bpp"/>
    <!--Identity-->
    <!--90-degreesCW-->
    <!--180-degreesCW-->
    <!--270-degreesCW-->
    <rotation value="Identity"/>
    <!--Identity-->
    <!--Centered-->
    <!--Stretched-->
    <!--Aspect Ratio Centered Max-->
    <!--Custom-->
    <!--Preferred-->
    <scaling value="Identity"/>
    <!--A value of 0/0 represents the optimal refresh rate. Scan-line-order must be Unspecified.-->
    <refresh numerator="108000000" denominator="1799408"/>
    <!--Unspecified-->
    <!--Progressive-->
    <!--Interlaced (upper field first)-->
    <!--Interlaced (lower field first)-->
    <scanlineorder value="Progressive"/>
</monitor>
<!--monitor:-->
<!--The id attribute must be specified.-->
<monitor id="54733568" adapterHigh="0" adapterLow="31682">
    <name>LEN L192p</name>
    <!--source: the origin of the video signal-->
    <source id="1">
        <name>\\.\DISPLAY2</name>
        <path>\\?\PCI#VEN_8086&amp;DEV_0126&amp;SUBSYS_21CE17AA&amp;REV_09#3&amp;e89b380&amp;0&amp;10#{5b45201d-f2f2-4f3b-85bb-30ff1f953599}</path>
    </source>
    <size width="1280" height="1024"/>
    <position left="0" top="0"/>
    <!--8bpp-->
    <!--16bpp-->

As you can see, this xml contains "width" and "height" that I want them to be changed, by constructing a function that the input will be monitor id, and the new resolution.

I wanted to start with finding the needed node but even that didn't work :

import clr
clr.AddReference('System.Xml')
from System.Xml import *
XMLDoc=XmlDocument()
XMLDoc.Load(r"C:\Users\myuser\Desktop\ThreeMonitors.xml")
t= XMLDoc.GetElementById("16843008")   ->> Returns "None"

Can anyone advise please? How to move ahead and what am I doing wrong?

thanks!!