Change date format on wordpress theme from US to UK

I have installed a Wordpress restaurant theme for a UK client. It has an online booking system. The booking itself is fine as it made on a graphic calendar, but the confirmation emails to both the (restaurant) clients and the restaurant go out in the US MMDDYY format which is confusing and could lose potential bookings. The theme designer says nothing can be done but it must show as DDMMYY.The site is at http://tempio.co.uk