To see your partitions and hard drives clearly, install the gparted program. The disk usage analyzer won't do it.
Oddly, when I installed gparted, it did not show up in the menu until I rebooted.
It is certainly the best idea to create a / partition, (which is where the operating system will be)
Then create a /home where all your personal stuff will be.
That will allow you to install a different operating system when you want to, leaving your personal files just as they were.
However, this is something that has to be done at the time that you install your operating system. You can't do it by simply renaming partitions.
Note: you only need about 8 GB at the most for the / partition.
Linux Mint 16 Cinnamon (64 bit), Quad core AMD A8-3870 APU with Radeon HD Graphics 6550D, 8GB DDR3, 1600MHz
Microsoft-free environment since 1996