1. Open your image in Adobe Photoshop
2. Select the crop tool.
3. Bring the cursor to any side of the image and press "Ctrl+Alt" and drag the side to whatever length you want the image to be
4. Hit enter.
5. Now select the "Rectangular Marquee Tool" from the toolbox.
6. Select the image completely covered from the top and make sure you leave the sides a bit for great results.
7. Then press "Ctrl+Shift+I" to invert the selection
8. Press "Shift+Backspace" and a fill pop-up will appear.
9. In "Contents" select "Content-aware" and hit enter.
10. Now press "Ctrl+D", the background will fill as per the image