A profile picture really personalizes your account! It's visible to you, your conversation partner and your followers on the Connect social feed. You can change that photo in your Profile tab from the left sidebar menu.
You can take a picture from your device by clicking on Upload Photo > Camera. Allow your browser to use your camera if needed, then click on Capture.
If the site won't let you upload your desired picture, you might need to revise it to a smaller format. Square dimensions are the best to prevent it from appearing pixelated. A photo that isn't uploading might also be in a non-traditional format so try converting it to .png and .jpeg).