Dear Duolingo somehow I can't change my profile picture does anybody have suggestions???
Maybe you are uploading a pic that is too big in size (> 1MB) or of a filetype that is not supported (e.g. I once tried uploading a new pic of the GIMP .xcf format, but that failed to change the pic).
Try uploading a .jpg file of a small size (under 100KB) and see if that works?