A partition on a disk (virtual or physical) cannot be split into different parts. This means after increasing the disk the adjacent free disk space is at the end of the disk (behind the last partition - H: in your case) and that's the reason you cannot increase G: What you need to do in this case is to use a partitioning tool to move the H: partition to the end of the disk to free up space adjacent to the G: partition. Then you can increase the size of this partition.
To do this you may use any of the tools mentioned in http://kb.vmware.com/kb/1004071
André