First, make sure you have a suitable file on your computer to use as a profile picture. For best results the picture should be square and be at least 648 by 648 pixels (the recommendation for Outlook profile pictures, since it's probably easiest to use the same one). Bigger is fine but don't go too small or it will be re-sized and probably look a bit fuzzy.
To add your profile picture on Glasscubes is fairly simple and quick. All you have to do is go to the top right corner of the page where your initials are and click on the arrow next to it.
Then click on 'Your profile'. When you click on it, you will be taken to a different page, and that page is where you'll be able to upload and change your profile picture.
Once you're here, you can click on 'Change photo' and this is where you can upload the photo of your choice to Glasscubes.