You can only rotate the photo in 90 degree increments.
Shrink or enlarge the original photo. When Gallery scales a photo, it maintains the same aspect ratio (height to width) of the original photo to avoid distortion. Your photo will be scaled until it fits inside a bounding box with the size you enter here.
Upload a new revision of this picture instead of the old one.
Note: The new file cannot be larger than 32 megabytes. If you want to upload a larger file you must ask your system administrator to allow larger uploads.
Gallery does not modify your original photo when rotating and scaling. Instead, it duplicates your photo and works with copies. This requires a little extra disk space but prevents your original from getting damaged. Disabling this option will cause any actions (rotating, scaling, etc) to modify the original.