Changing permalinks from /promotions/

There is not setting for that, but it can easily be altered with a bit of code:

add_filter( 'wp_ps_promotion_post_type_args', 'change_ps_promotion_slug');
function change_ps_promotion_slug( $args ) {
    $args['rewrite'] = array( 'slug' => 'downloads' );
    return $args;
}

Placing this code in a custom plugin or in your active theme’s functions.php file should do the trick.

NOTE: After adding this code, it will be necessary to flush the rewrite rules. This can be done by visiting the ‘Permalinks’ page in the admin.