If the photo you want to use for your profile is too zoomed out or has a background you'd rather not include, you can crop the image using a free online tool such as this one on iloveimg.com.

Simply drag and drop the image you want to crop, and adjust the selection as desired.

If you want to keep the image roughly square, try to ensure that the "Width" and "Height" on the right-hand side are as close as possible.

When you're done, hit "Crop Image" and then "Download"