As a PreprLabs user, you can cancel a Challenge by deleting your project. For a step-by-step guide on this, check out the following article: How to delete a project on PreprLabs

As a PreprLabs Lab Manager, you can either delete the Challenge or Close the Challenge.

To delete the Challenge, go to Manage Challenges.

Click on the Manage Button for the Challenge you want to delete. Click on Delete Challenge.

To close a Challenge, click on Edit under the Challenge Manage button.

On the Edit Challenge page scroll down the page and change the Status to Closed.