Hi:
I installed Win7 32 and Win7 64 on partitions "C" and "D" respectively.
Please clarify...
You had two Win7 systems installed initially, clearly into two separate partitions. But if you did install each one in the standard way (i.e. booting using the Win7 installer DVDs for x86 and x64 and proceeding), then each system would install itself as C, when you actually booted to that installed version of Windows.
And there was a Boot Manager, and boot menu, that showed both versions of Windows as bootable. Yes?
Now aside from C (which Windows always assigns to the boot partition), once booted to Windows any other partitions present would then normally be lettered sequentially starting with D, E, etc. So if you booted to x86 Win7 its own partition would appear as C, and the x64 Win7 partition would appear as D. But if you instead booted to x64 Win7, then it would also appear as C with the other x86 Win7 partition appearing as D.
In other words, the C partition is the "boot partition" for the operational Windows. Any other partitions visible while still booted to that operational Windows are assigned D, E, etc. There is no actual fixed drive letter assignment to specific partitions, and in fact you can even use DISKMGMT.MSC to change the assigned drive letters for all partitions other than C, to meet your needs. In fact this drive re-lettering after-the-fact is commonly done when having multiple bootable Windows systems, to eliminate user confusion so as to have all additional partitions lettered identically no matter which Windows system you're booted to. Of course you can't re-letter the booted Windows, as it will always be C when you boot to it.
A sensible compromise (in order to avoid confusion the best possible way) if you have two bootable Windows partitions along with other partitions, is to re-letter the other Windows partition as D in both Windows system. So you'll always be booted to C no matter which Windows you boot to, and the "other" Windows will always be D no matter which Windows you boot to. And then for BOTH Windows systems, assign drive letters for any additional partitions you might have starting with E, F, etc.... IN BOTH WINDOWS SYSTEMS. That way, no matter which Windows you're booted to, all of your "data" partitions are consistently lettered E, F, etc., the booted Windows is always C, and the "other" Windows is always D. Keeps things consistent and easily navigated, no matter which Windows you are running with.
Now, back to my question. When booted to the x64 system you've retained (on that second partition), the partition itself does appear as C, right? It does not appear as D, right? It was only D when you were previously booted to the x86 system (which to itself was also C).
And if so, and if you originally had a Boot Manager running to offer you the option of choosing either of your two bootable Windows (x86 and x64) from the boot menu, how did you actually remove the unwanted x86 Windows on the first partition? What happened in the boot menu? Did you remove the entry for the deleted x86? Does booting occur properly now for the single remaining x64 system? How did the boot menu entry get removed for the now-gone x86 system? Did you use something like EasyBCD, or what??
So all you want to do is physically "slide left" that second x64 partition, to physically occupy the space formerly occupied by the x86 Windows partition. Right?
Again, my recommendation is to use Partition Wizard for this easy-to-do maintenance.