Hi Ramesh.Ottawa,
First you will need to ensure you have enabled manual ranking correctly. Please click on the "Options" icon in the right hand menu system. Then select the "Input" tab and make sure both "Display ranking information" and "Allow manual ranking" are selected.
Click on "OK" to close the Options dialog.
You should then see a faint ranking icon in the top left of each image. Click on the image you wish to modify to zoom in, and move the mouse cursor over the ranking icon - it will become brighter, and you can then click on it until you have the ranking option
you require.
Let me know if you need further advice.
Thanks,
Chris.