To go from 32 Bit to 64 Bit you need to clean install. See here:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/

You would lose everything with a clean install and might have to buy the 64 bit win 7 disk to change unless you received both disks from Dell--really not worth the expense for little difference in performance. Stick with 4 gb and 32 bit. 

You cannot upgrade Windows 32-bit to 64-bit. It's not supported. You need to perform clean install only. The following link will be helpful: http://windows.microsoft.com/en-us/windows/32-bit-and-64-bit-windows#1TC=windows-7

Kindly note that the same product key can be used for both the architectures (i.e, same product key can be used for 32-bit as well as 64-bit installations, in the same PC). You can also have 64-bit and 32-bit Windows installations in the same PC parallely.

Additionally, you can use Windows Easy Transfer to migrate most of your files to 64-bit. Refer the link for more information: http://windows.microsoft.com/en-us/windows/transfer-files-settings-from-another-computer#1TC=windows-7

A clean install without reformatting will archive the original Windows installation in a Windows.old folder, and everything else will remain as-is.

The suggestion of Windows Easy Transfer is spot-on. As for a 64-bit install disk, an image can be downloaded from Digital River, and either burned to DVD or used to create a bootable flash key.

Keys are not locked to an architecture they are interchangeable.

Thank you all for your help. I will try the update from 32 bit to 64 bit as it sounds like a challenge and I will get the 8gb performance. Just one more thing...if I did download the win pro 7 64 bit, can I still use the win pro 7 32 bit product key to activate windows or do I have to buy another key? Many thanks. Sid

In my previous post, I've explained about the compatibility of the product keys across architectures.

But the images can be used with the available product key present in the COA label on the laptop.

Thank you all for your help. I will try the update from 32 bit to 64 bit as it sounds like a challenge and I will get the 8gb performance. Just one more thing...if I did download the win pro 7 64 bit, can I still use the win pro 7 32 bit product key to activate windows or do I have to buy another key? Many thanks. Sid

When migrating from 32 Bit to 64 Bit Windows using a Digital River .iso ensure that you use the Activation Backup and Recovery to Backup your Dell BIOS System Locked Preinstallation Key before the install:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/microsoft-product-activation/the-activation-backup-and-recovery-program-windows-vista-7-version/

Once you have clean installed Windows 7 you can use the utility to restore your DELL BIOS System locked Product Activation.

Note the activation files made from the backup will only work on a eligible Dell BIOS.

This will save a tedious call to an automated Microsoft Activation Centre.

For details on downloading the .iso from Digital River see here:

http://dellwindowsreinstallationguide.com/download-microsoft-windows-and-office/download-microsoft-windows/windows-7-sp1-iso-download/

You may use Rufus to create a bootable USB with the .iso which is meant to have less hassles than the official Microsoft tool. In your case you want the default settings "MBR Partition Scheme for BIOS or UEFI Computers":

http://rufus.akeo.ie/

My A Clean Install of Windows Guide will give additional instructions regarding the Windows installation:

http://dellwindowsreinstallationguide.com/a-clean-install-of-windows/

an image can be downloaded from Digital River, and either burned to DVD or used to create a bootable flash key.