I have searched for the answer to this problem for a while. I have a 64GB flash drive that I recently had to format to FAT32 to place Windows Recovery tools on it.
When I attempted to extend the re-reformatted exFAT partition to its original 64GB state with the Disk Management window, it would not allow it. I learned that Disk Management could only extend NTFS partitions.
I temporarily reformatted the disk to NTFS and ensured the partition in question was on the right, but still I am unable to extend the volume. The option remains "greyed out."
Here's a partial screenshot of the drive in Disk Management (click to zoom in):
Is there something I'm missing to extend the drive in question?