As you do this, you should keep your instagram profilbild zoom eyes open for people trying to scam you. You can tell if they're trying to do this by the way they take their pictures. So take your time before you click on it.
The correct size for an Instagram profile picture is 110 x 110 pixels and must conform to Instagram's 4:5 aspect ratio. In addition, you should remember that your image will not appear as a square in the mobile or web app, so you must leave a space in the corners.
You can resize your image by going into the settings for the Instagram app and changing it. This is a good way to ensure your photos look their best and to give you a chance to make the necessary edits before posting them online.