#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %hash = ( 'key1' => 'test1',
	     'key2' => 'test2',
	     'key3' => 'test2',
    );

print Dumper \%hash;

$hash{'key4'} = delete $hash{'key1'};

print Dumper \%hash;

__END__

$ perl test.pl
$VAR1 = {
          'key1' => 'test1',
          'key3' => 'test2',
          'key2' => 'test2'
        };
$VAR1 = {
          'key2' => 'test2',
          'key3' => 'test2',
          'key4' => 'test1'
        };