use warnings;
use strict;
use XML::LibXML;

my $doc = XML::LibXML->new->parse_fh(\*DATA);
# or ->parse_file("news.xml")

my $root = $doc->getDocumentElement;
my @nodes = $root->findnodes("new");
$root->removeChild($nodes[-1]); # Remove the last.

print $doc->serialize();# Or... print $root->serialize();

__DATA__
<listaNews>
    <new>
      blah blah blah
    </new>
    <new>
      blah blah blah
    </new>
</listaNews>