Use Minitool partition wizard. It will allow you to achieve this.
It is pretty simple. If you cannot figure out how to do it, I can expand this answer.
Apparently, minitool wont let you merge partitions unless you purchase pro version.
I found a different software: http://download.cnet.com/Easeus-Partition-Master-Free-Edition/3000-2248_4-10863346.html
They have a tutorial for merging partitions. I will summarize the steps:
From the screenshot above, I think the partitions are adjecent on disk(unless you have manipulated the screenshot)
- Open the tool and select your partition E:
- Right click and select Merge Partition.
- Choose partition G:.
- Select the destination partition and click Ok and then Apply.
- This should merge your partitions
You can find the full tutorial here(they also have a video):http://www.partition-tool.com/easeus-partition-manager/merge-partition.htm