You can add a new photo in your profile settings.
Desktop version:
Please log in to your account and click the portrait icon in the top right corner of the page, then select “Your profile” from the menu. This will take you to the profile page. Click on the plus icon to add a new photo.
Mobile version:
Please log in to your account and click the portrait icon in the top right corner of the page, then select “Your Profile” from the menu. This will take you to the profile page. Click "View my profile" button, scroll down a page a little and click on plus sign in Photos section to add a new picture to your profile.
Please note that the size of each file should not exceed 7MB. Additionally, images must not be smaller than 333 by 333 pixels. Acceptable file formats are JPG, GIF or PNG.
If you are still unable to upload a profile photo, please follow the instructions in this article.