You can amend how many tickets you have on sale at any point before the ticket closes. To do this head to your ticket overview screen: https://promotioncentre.co.uk/tickets-overview.php
From there scroll down to the ticket you would like to adjust, then in the Action column at the end of the ticket row, click on the pencil icon.
On the next screen, in the Tickets Available box, Change your allocation to your new number.
Then scroll to the bottom of the page and hit ‘save’ - your new allocation will update immediately.