function change_proceed_to_checkout_text( $button_text ) {
return __( 'Proceed to Payment', 'woocommerce' );
}
add_filter( 'woocommerce_order_button_text', 'change_proceed_to_checkout_text' );
add_filter( 'woocommerce_checkout_order_review', 'change_proceed_to_checkout_text' );