People are able to update their details after they register, for example to upload a photo, by clicking on the link at the bottom of their confirmation email.
If they no longer have their confirmation email, the website admin can resend it to the email address they registered with. This article explains how to do this.
First, navigate to your Dashboard at the top left-hand of the screen and click in the Online Registrations tile.
Click on the registration form name to view the list of people registered. Next, click on the person's name to edit their record and select the Resend Registration Confirmation Email button.
Now, the person can click the link at the bottom of the email to modify their registration details.