One easy way to disable the reviews tab in WooCommerce is to edit the themes functions.php file. Add the following to the end of the file:

add_filter( 'woocommerce_product_tabs', 'sb_woo_remove_reviews_tab', 98);
function sb_woo_remove_reviews_tab($tabs) {

 unset($tabs
['reviews']); return $tabs; }

You can access the functions.php from most self hosted WordPress installations by navigating to Appearance > Editor then selecting the file on the right hand side.