You are able to withdraw your entrants directly from the system.
From the ENTRIES page, find the athlete you wish to withdraw and then click the basket icon on the right.
This takes you to the basket page. You will see the basket for the person who made the entry so there may just be one athletes or there could be plenty. Select the athlete you wish to withdraw by checking the tick box to the left of their name:
Then click the red dustbin icon and confirm the removal:
You will then get confirmation via an updated basket:
The athletes will be removed from the Competitor page.