To update your profile photo manually, start out by logging in, then navigate to your profile page and look for the "Actions" button underneath your current profile image placeholder. Click this button to expand a drop-down menu and click "Change Picture."
This will open up an image upload wizard. From here you can select an image from one of many services (everything from Dropbox to Instagram!) or upload an image from your Desktop. To do the latter, drag your photo to the center of the screen or click the button to upload a photo.
Your photo will show in the upload wizard, and you'll have the opportunity to crop, rotate, and even sharpen or blur the image. Once it looks right, just click save and you'll be all set!