1. Go to evenium.com
2. Click on My Events
3. Click the name of the event under the I Organize section
4. Go to the Participants tab located on the purple bar
5. To edit a participant record, simply click on their last name and update the information as necessary in the panel that opens on the right. 
6. If you need to do bulk updates, check the box left of the name of desired participants and click on the Modify button at the top