If you want to change your site preferences including your photograph simply, Login, then click on your name.
When you upload a photograph the website takes a square from the middle of the image to make your icon. So for best results make sure you are roughly in the middle of the image. Or better still edit the image and make it square before uploading.
If you are leading a walk or you are the contact for an event it is important that people know who you are. So upload your photo now!