I have tried some post-processing with your picture : after that it is obvious for me that one major problem is the over-compression of the picture.
Try uploading the original picture, exactly the one you have extracted from the storage card of your camera. If this one is also overcompressed, then next time you take pictures, you should choose in your camera setting the highest resolution - lowest compression option. Don't try saving this .bmp (?)picture in a jpeg file, as it would be even worse.
Concerning the bad level, I'm not 100% sure, but I would rotate the picture to the right by 0.5° or 1°.
What do you think I should crop?
the aircraft is too small compared to the entire picture, crop from the left until the airport tower, and from the right so that it will be about 1cm left between the aircraft and the right frame of the picture. Try to keep approximatively a 3/2 lenght/height ratio. Crop also this ugly orange "19.09.2004"
Where do you get photoshop ?
you can get it on computer shops, however it is quite expensive. You can also use another picture editing program.
Once again, the major problem is that the quality of this picture is bad, I think mainly because of the too high compression. If you can give me a less compressed file, maybe I can process it for you with photoshop.