32-bit consumer-editions of windows won't use physical memory above 4GB. What you are asking for can't be done.
If you have more than 4GB of physical memory, upgrade to 64-bit Windows. 64-bit Windows is faster and you can still run 32-bit programs. The only thing you lose by upgrading is you will no longer be able to run 16-bit programs natively in Windows without a VM (but you probably weren't doing that anyway, right?)