Ler xml e alterar elemento (VB.NET)

[BorgesAltair]

Olá amigos,

 Preciso ler um XML, localizar os elementos  t51 (protocolo) e substituir seu conteúdo.

 Infelizmente o XML não tem abertura/fechamento padrão das TAGs.

Abaixo o XML em questão.

<?xml version="1.0" encoding="ISO-8859-1"?>
<retorno>
<hd h01="0" h02="341" h03="ITAU UNIBANCO SA" h04="18112014" h05="SDT"
h06="BFO" h07="RTP" h08="000001" h09="0005" h10="" h11="" h12="" h13="659608"
h14="043" h15="5300108" h16="" h17="0001" />
<tr t01="1" t02="341" t03="0355068206/6596" t04="" t05="" t06=""
t07="" t08="" t09="" t10="" t11="191-82762218-1" t12="" t13="" t14=""
t15="" t16="001" t17="00000000065021" t18="00000000065021" t19="" t20=""
t21="" t22="" t23="" t24="" t25="" t26="" t27="" t28="" t29="" t30=""
t31="10" t32="0000008141" t33="2" t34="07112014" t35="0000008924" t36=""
t37="17112014" t38="" t39="" t40="" t41="" t42="" t43="" t44="" t45=""
t46="" t47="" t48="" t49="" t50="00000000000000" t51="101" t52="0002" />
<tl t01="9" t02="341" t03="ITAU UNIBANCO SA" t04="18112014" t05="00005"
t06="000000000000384268" t07="" t08="0007" />
<hd h01="0" h02="237" h03="BANCO BRADESCO S A" h04="18112014" h05="SDT"
h06="BFO" h07="RTP" h08="000002" h09="0001" h10="" h11="" h12="" h13="100320"
h14="043" h15="5300108" h16="" h17="0001" />
<tr t01="1" t02="237" t03="003702800087637" t04="" t05="" t06=""
t07="" t08="" t09="" t10="" t11="009134246006252" t12="" t13="" t14=""
t15="" t16="001" t17="00000000040000" t18="00000000040000" t19="" t20=""
t21="" t22="" t23="" t24="" t25="" t26="" t27="" t28="" t29="" t30=""
t31="10" t32="0000008144" t33="1" t34="11112014" t35="0000000000" t36=""
t37="14112014" t38="" t39="" t40="" t41="" t42="" t43="" t44="" t45=""
t46="" t47="" t48="" t49="" t50="00000000001500" t51="102" t52="0002" />
<tl t01="9" t02="237" t03="BANCO BRADESCO S A" t04="18112014" t05="00001"
t06="000000000000040000" t07="" t08="0003" />
</retorno>

Alguém sabe como resolver isso? 

Altair Borges