If you'd like to remove your collage you'll have to delete the HTML code.
The HTML code is usually displayed in the "About Me" or "My Interests" section of your profile.
What you need to do is go to "Edit Profile" and find one of the above categories. You'll recognize the HTML code for the collage because it has MyHeritage written in it somewhere.
What is important, is to delete ALL the code, but not to delete code from other things you've added to your profile. The HTML code for your collage should begin and end with the same symbols - <p> is the most common one.
What I suggest you do is to cut/paste the code to a word doc or something and then go back and view your profile to make sure you got the right code. That way you haven't deleted anything important by accident. And you can save your collage if you want to post it at a different time.