If the ZWave USB stick installed on your C-5 is white on one side and grey on the other, that manufacturer did not produce sticks that are readable. Some parts of the world got a ZWave USB stick that is all black and is readable.
Because of Murphy's Law, I'm going to guess you have the white/grey Nortec UZB stick and will have to do a manual migration. I've done two of them and it's tedious but not hard.
You start by thinking about it and making a plan. The issue is to prevent overlapping ZWave DNI.
On your C-5, start by counting the total number of ZWave devices that you will be migrating. Let's use "30" for this example. Look at Settings: ZWave Details and notice the Node numbers.
The first device you manually migrate to the C-8 will join as Node 6. (Nodes 1-5 are reserved.) You don't want to have an already existing Node 6. Same with the next..
If there are 30 devices to migrate, and you follow the Exclude-before-Include advice, you will Join the last device with a Node of 36. Which means you need to plan out how to prepare the C-8 for those first 36 Node IDs. You're going to migrate from the C-8 outwards, powered devices before battery devices, so the numerical order on the C-5 isn't important. Snap a picture of those first "30" devices so you can find them in the next step, by Name.
Power off the C-5 and power on the C-8. In Devices, go through all the ZWave devices and put "old" at the end of each name. If that device IS PART of the "30" to be protected, put a "x" at the beginning of the DNI (click edit to change it) and save the device. You will "touch" every Zwave device in the list adding old to the end of the name AND maybe adding an x to some DNI's.
Now migrate your devices one at a time. When it's time to name them, use the original name. Then, after testing the new device to confirm working in Device Info, use Settings: Swap Apps Device.
Select the device with "old" in the name on the left, select the new device on the right and click Swap old device in all apps This will do exactly what it says, it will move all the InUse by items at the bottom of the old device to the new device. You can now delete the "old" device.
Rinse, repeat. Note that the "protected" devices have a DNI that is invalid and thus it won't delete immediately. Click Force Remove for those. (This is why my advice is to protect only the first "30" because for non-overlapping Node IDs the Remove goes quickly, no Force required.)
NOTE: replace "30" in this advice with your Actual number. For me, I found I had very few overlaps. Over time, I had replaced older devices with new and thus the old low Node numbers no longer existed. In one case I had 28 devices to move and there were zero devices between Node 9 and Node 41 and so I only had to "protect" those first few.)
This is what "old" is doing for you...
Which one is the "old" device?? They are both in the list with the same name. By starting the process with renaming all the devices you know you're going to delete, you make the Swap Apps Devices process a lot simpler.
I learned this process during my first migration... and you can be assured I learned the hard way about overlapping DNI. The last half of the first hub and all of the second hub I migrated went very smoothly when I followed this method. 
