You can delete an activity with the following instructions:

1. Sign into your account at grokker.com
2. Access your "My Profile" by clicking on your avatar icon in the top right corner of the the home page
3. Click on the tab "I Did This" and locate the activity you would like to remove
4. To the far right of the “I Did This” post, click on the arrow and then click DELETE to remove the "I Did This" post