Change from 10 to whatever:
back up wp-admin/includes/media.php
find this:
$start = ( $_GET['paged'] - 1 ) * 10;
if ( $start < 1 )
$start = 0;
add_filter( 'post_limits', create_function( '$a', "return 'LIMIT $start, 10';" ) )
and this:
$page_links = paginate_links( array(
'base' => add_query_arg( 'paged', '%#%' ),
'format' => '',
'prev_text' => __('«'),
'next_text' => __('»'),
'total' => ceil($wp_query->found_posts / 10),
'current' => $_GET['paged']
));
and change 10 to 50 or 100 or ...