c# xelement change attribute value

gistfile1.cs

<Root>
<Address myatt="abc">NY</Address>
<Address>AUS</Address>
</Root>

if (myXelement.Element("Address").Attribute("myatt").Value == "Abc")
{
  myXelement.Element("Address").Attribute("myatt").Value = "XYZ";
}


or

if (myXelement.Element("Address").Attribute("myatt") != null)
{
    myXelement.Element("Address").Attribute("myatt").Value = myXelement.Element("Address").Attribute("myatt").Value + " appended;";
}
else 
{
    myXelement.Element("Address").Add(new XAttribute("myatt", "Added"));
}