use strict;
use warnings;
use XML::Twig;

my $xmlStr = <<XML;
<Requests>
  <Request ToDir="FTP54">
    <TypeA>
      <fileNumber ID="54" />
    </TypeA>
  </Request>
  <Request ToDir="FTP78">
    <TypeA>
      <fileNumber ID="78" />
    </TypeA>
  </Request>
  <Request ToDir="FTP79">
    <TypeA>
      <fileNumber ID="79" />
    </TypeA>
  </Request>
</Requests>
XML

my $twig= new XML::Twig(
    twig_handlers => { Request => \&request }
);
$twig->parse($xmlStr);
$twig->print();
exit;

sub request {
    my ($twig, $req) = @_;
    my $name  = $req->att('ToDir');
    $req->delete() if $name eq 'FTP54';
}