Windows 7 comes in 32-bit or 64-bit versions. These versions reflect the capabilities of central processing units (CPUs), which use 32-bit or 64-bit instruction sets. 32-bit processors can address up to 4GB of random access memory (RAM) maximum, but 64-bit processors can address up to 16 billion GB of RAM.
To convert Windows 7 32-bit to Windows 7 64-bit, confirm that the CPU installed to the PC uses a 64-bit instruction set. If the computer has a 32-bit CPU, Windows 7 64-bit won't run.
Download, install and run CPU-Z (cpuid.com/softwares/cpu-z.html). Click the "CPU" tab to view the name and model of the processor installed in your computer.
Navigate to the CPU manufacturer's web site and look up the product model. Check the information shown next to the "Instruction Set," "Data Width" or "Operating System" field to determine whether the processor uses 32-bit or 64-bit technology. If the processor uses a 32-bit instruction set, you can't convert Windows 7 32-bit to a 64-bit OS.
Copy any personal files on the hard drive to another storage device, like an external USB drive.
Navigate to your motherboard or computer manufacturer's web site and look up your computer or motherboard model. Download the 64-bit drivers for your PC and burn the drivers to CD.
Insert the Windows 7 64-bit DVD into the disc drive. Restart the computer. Select your language, regional and keyboard options.
Click "Next." Click "Install Now." Read the Microsoft Software License Terms. Check "I Accept the License Terms" if you agree.
Click "Next." Click "Custom (Advanced)." Choose the hard disk installed with Windows 7 32-bit.
Click "Drive Options (Advanced)." Click "Format," then click "Next," to begin installing Windows 7 64-bit over Windows 7 32-bit. Do not touch the keyboard even if the screen prompts you to press a key to boot from the DVD.
Enter a computer name and account name on the "Set Up Windows" screen. Click "Next."
Input an account password, if desired, then click "Next." Input your Windows 7 product key. Follow the remaining on-screen instructions to finish setting up the installation.
Click "Start." Input "devmgmt.msc" (without quotes) into the search field and press "Enter" to open Device Manager. Click the arrow icon next to each category to view the installed devices.
Look for any devices marked with a yellow exclamation mark, which indicates a device driver error. Install the device's 64-bit driver from the disc you created earlier.
To install a device driver from the CD, double-click the appropriate EXE file to launch the set-up program. Some device drivers use the INF format. To install a driver from an INF file, right-click the file, then click "Install."