Something like this should do the trick:

sub wanted { 
    rename($_, lc) or die "$_: $!" if !-d && /[A-Z]/;
}
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To change the links is a bit tricker. I'd recommend using something like HTML::TreeBuilder and code like:

my $tree = HTML::TreeBuilder->new_from_file($fn);
foreach my $a ($tree->lookdown('_tag', 'a')) {
  $a->attr('href') = lc($a->attr('href'));
}
open OUT, ">$fn" or die "Can't overwrite $fn ($!)";
print OUT $tree->as_HTML;
close OUT;
$tree->delete;
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Hope this helps.

gav^