I have 32 bit windows 7 home premium, can I shift to windows 8 64bit?
I have legal purchased windows 7 home basic > upgraded to windows 7 home premium.
Now I have 8GB ram, so want to shift to windows 8 64bit.
Can i surrender my 32bit windows 7 cd key and upgrade to windows 8 ?

You will have to do a clean installation, there is no in place upgrade path from Windows 7 32 bit to Windows 8 64 bit.
when you receive the Windows 8 DVD, install the Windows 8 Windows Easy Transfer Utility from the DVD (To find it, just navigate to x:\support\migwiz, 'x:' represents the name of your disk drive. In this folder, you will see a collection of files, the important one you need to look for and double click is 'migsetup'.) , run it and create a WET file (Windows Easy Transfer file), if you have an external hard disk, you can have it stored there so you can access it later when you do a clean install of Windows 7 Professional DVD.
Once you have done that, simply do a clean install of Windows 8 DVD. In Windows 8 DVD, launch Windows Easy Transfer, follow the on screen wizard, point to where you stored the the WET file (external hard disk), and it will restore your personal files and settings. Reinstall any necessary applications.