Open photo with your photo software
Then click on options or tools and select resize. It is typically grouped with "rotate" image.
When resize window opens select "pixels" some images open with "inches' as the size reference.
When you see Pixels, select 200 or change to 200. Make certain that image is 200 in both directions, (heigt and width)
Then you save the image.
Now you can upload image to your new avatar.
If you need more assistance send photo to me in email and I will fix for you. My email is email@example.com