If the tag is same for all the elements, try this also

use strict;
use warnings;

use Data::Dumper;

my @array=('<NumData>1234</NumData>','<NumData>543535<NumData>');

my @Output;
foreach my $data(@array){
    $data=~ s/<NumData>|<\/NumData>//g;
    push @Output, $data;
}

print Dumper @Output;
[download]