b) use the Partition Manager to MERGE both partitions then APPLY to finalize the procedure (it may reboot and take a while to sort this out). It should keep the data from G intact, but if it warns you that you'll lose data then don't do this unless you can copy the data. Also, if you have any programs installed to G (normally not) they won't run if you merge the two partitions.
I also recommend moving anything in G-drive in a single folder that you can easily access once the two drives are merged. (If a folder is at G:\Media it will be turned into C:\Media).
*If your system is pre-built you likely have a HIDDEN PARTITION containing a backup copy of Windows. I recommend you don't delete this.