Go to http://www.amazon.com/ and sign in.
navigate: Kindle Index || About The Book || Book Suggestions
Use Back button or Home to return to Kindle
Click Here For Free Kindle Reading Applications for PC, Mac, iPhones etc.
Re-Downloading an eBook from Amazon
Scroll to Digital Content and click Manage Your Kindle
Sign in again
Scroll down to locate the eBook you want to re-download.
Hover the cursor over or click on the button labeled Actions.
This will bring a pop-up window. Select "Deliver To My..."
This will bring a popup window to Deliver Title.
Use the pull down menus to select the method and destination for your download, and click on Deliver.
If you want to use "Download and transfer via USB" and plan to transfer it to your Kindle, make sure your Kindle is attached to your computer and that clicking on its icon on the desktop will open it as a drive with a subfolder called "documents". If there is no icon on your desktop, find it by double-clicking on My Computer (in Windows) and then clicking on Kindle.
Click on Actions, then click on "Download and transfer via USB"
This will bring the Download and Transfer via USB popup window.
Choose "Save As", browse for the Kindle drive, select the folder labelled "documents", click on Open and then Save.