To change dates, or shorten your booking, go to
https://www.speedybooker.com/mybooking/. Enter your reference number and password as found on the confirmation email, or log in to your account if you have one, and you can make your amendment (if this option is available) from there by clicking Amend my booking, then changing the dates required and adding or removing the rooms required.
Please note amendments are allowed only if availability exists and some non-refundable rates are not amendable.
Alternatively, to extend your booking, you might find it easier to make a fresh booking through the site, and make a note in Additional Information that you would like to keep the same room, please note that although the accommodation will try their hardest to accommodate your request, retaining the same room is not guaranteed.