Use this free image editor: https://pixlr.com/x/
Load image to editor:
- Drag and drop, or choose file to upload.
- Choose the maximum definition provided.
Rotate and Crop
- Rotate first, if necessary.
- Open Crop Window
- Enable "Select Aspect" (it will default to square ratio).
- If Square works for the image, save to continue.
- If Square doesn't work - disable the Select Aspect feature, then drag and drop box edges to get as close to square that works with the image, then Save.
Save as High Quality Jpg
- Rename file to a user friendly name.
- Change one of the dimension boxes to 750 (the other will update when the cursor leaves the box) - this reduces the image size so it will load quickly.