How to Make A Picture Smaller To Fit A IPhone 5 WallPaper?

The photo I want to put on my lock screen is too big and I can't really crop anything out because it would take out important parts of the picture. Is there anything I can do to make the picture as a whole smaller? All answers are helpful thank you in advanced.

You can download instasize to help! It will make the image smaller! It's easy to save and set as your wallpaper.