How can I remove the namespace of header node using C#

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C#

XML

Is there any possible way to read data of child nodes of xml below. Because of the header node's namespace, i cant read inner node's values

<?xml version="1.0" ?>
<Header xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<H1>A</H1>
<H2>B</H2>
<H3>C</H3>
<H4>D</H4>
</Header>

without namespace of header node's like below can reads values of inner nodes. Any advice please

<pre><?xml version="1.0" ?>
<Header>
<H1>A</H1>
<H2>B</H2>
<H3>C</H3>
<H4>D</H4>
</Header>

What I have tried:

I tried to replace the header node and still no any progress