Greetings,
The 970 is supported on your board 128GB~1T
"D" is the upper slot
"A" is the lower slot
Charts on page 17. Since the board does not have an unlimited number of resources or lanes available, certain installations "share" resources. This is why you see "check marks" in some areas and "x's" in others. It's also why you see PCIe x4 SSD runs at x2 speed if you run in the "D" upper slot.
Suggest you install in the lower slot "A". Here's why:
You will get full x4 performance from your 970
You will have use of all SATA and SATA Express connectors (if you wish)
Drive will run a little cooler since it won't be behind or near your GPU
If you want to migrate your OS, here's what you are going to do.
Create a full back up image of your windows OS
Shut down and disconnect power to your your SSD
Install the NVMe 970
Start the system, enter BIOS and ensure the NVMe device is present
Restart again
Use a bootable USB or CD to restore the image you made of your OS
Now your system is booting from the new storage
Shut down and reconnect power to your old SSD
Boot into windows, open an administrative command prompt
type diskpart, press enter
type list disk, press enter
type select disk x (Note x is an example be sure to select the correct number)
Disk x now selected
type clean, press enter
type convert gpt, press enter
Finally,
type create partition primary, press enter
type select partition x (Note x same as above example)
type active, press enter
Close the command prompt and assign a drive letter.
Hope this helps.