How to remove specific data line from html file with Ruby

How to remove specific data line from html file with Ruby

i have a file name payment.html.erb
content have:
<form method="POST" action="http://www.example.com" id="my_id" class="form">
<input type="hidden" name="Timestamp" value="2013-09-29T08:05:14.Z"/>
<input type="hidden" name="Signature"
value="dd01adafd2689b243d6cbc9088da2bf699976eb0"/>
<input type="hidden" name="Amount" value="1"/>
<input type="text" name="AccountName" value="" placeholder="account name"/>
<p></p>
<select name="ExpireMonth">
<option value="8">8</option>
<option value="9">9</option>
<option value="10">10</option>
<option value="11">11</option>
<option value="12">12</option>
</select>
<select name="ExpireYear">
<option value="2017">2017</option>
<option value="2018">2018</option>
<option value="2019">2019</option>
<option value="2020">2020</option>
</select>
<input type="submit" class="yyy" id="xxx" value="submit"/>
</form>
i am reading from file and again need to write back into file (i already
coded)
i want remove all non hidden html fields and also 'Form' starting tag and
closing tag.
thanks