C# - XDocument Change All Attribute Names?

I have an XDocument that looks similar to

<root>
<a>
<b foo="1" bar="2" />
<b foo="3" bar="4" />
<b foo="5" bar="6" />
<b foo="7" bar="8" />
<b foo="9" bar="10" />
</a>
</root>

I wish to change the attribute foo to something else, and the attribute bar to something else. How can I easily do this? My current version (below) stack overflows with large documents, and has an awful smell to it.

string dd=LoadedXDocument.ToString();
foreach (var s in AttributeReplacements)
dd = dd.Replace(s.Old+"=", s.New+"=");