Adding photos of yourself and your staff is a great way to make your profile more personal and will increase the likelihood that fellow business owners will reach out to you, as it is always nice to put a face to a business.
Navigate to your business page by either clicking "My Business" in the left-hand menu or from the dropdown in the upper right. Scroll down to the section that reads "Our Team".
Click the blue "Edit" link next to the user whose photo needs to be added or updated. Once on the "Edit User" screen, click the blue "Upload Image" button to browse your computer's files for a photo to use. Please note: this photo needs to be square (182x182).
Click "Update User" when you've updated the photo to save your changes.