Need help with HD EXTERNAL DRIVE FORMATTING FROM PC TO APPLE

I RECENTLY TRANSFERED ALL MY PICS AND VIDEOS ON TO WD 3.0 MY BOOK ESENTIAL FROM A WINDOWS 7 PC   NOW I WANT TO CONVERT OR TRANSFER THEM TO A IMAC OS 10.5  AND AFTER THAT I WANT TO TRANSFER ALL PICS FROM FROM THAT IMAC THAT ARE NOT FROM PC ALONG WITH THE PC ONES TO WD HD    HOW DO YOU DO THIS WITH OUT EVERYTHING DELETING 

NEED YOUR HELP

Welcome to the Community.

In order to have the hard drive working on both Windows and Mac OS you’ll have to format the hard drive as FAT32, which will delete all stored data. I’d empty the hard drive’s content first on the Windows computer before proceeding to format the hard drive.

http://wdc.custhelp.com/app/answers/detail/a_id/291/