#!/usr/bin/perl
use strict;
use warnings;

my %hash = ('Key1' => 'Value1', 'Key2' => 'Value2');
print "$hash{Key1}\n"; # print 'Value1'

foreach (keys %hash) {
    $hash{$hash{$_}} = $_;
    delete $hash{$_};
}
print "$hash{Value1}\n"; # print 'Key1'