I had trouble finding information about upgrading firmware for my unit and reading all the horror stories, was a bit worried about bricking mine. So here's a log of my experience hoping it helps someone.
My unit is the "international" version (I'm from Australia) and was bought from ebay.
from:
DS-7608NI-I2 / 8P
V3.4.93 build 170408
to:
DS-7608NI-I2 / 8P
V4.1.70 build 181114
Before:

I downloaded:
NVR_K51_BL_ML_STD_V4.1.70_181114.zip
From:
DOWNLOAD EU PORTAL
I did the upgrade locally on the NVR with a monitor connected. Unzipped the downloaded file to a USB, insert USB to NVR and did the upgrade via the GUI.
Seemed to work OK, upgraded normally.
After:

So far so good, logged in via web OK, settings seem to have been retained. I'll update the thread with any issues as I bring up the cameras and attempt to get it back operational.
Update 1:
Cameras added OK
Some settings (schedules for motion/line crossing detection) were lost
I tried adding a "NAS HDD", which has never worked for me - part of doing the upgrade was to fix this, looks like it's worse. After I add a NAS HDD (FreeNAS NFS share), I get HDD Exception, unit beeps and enters a boot loop of constant restarts. Disconnecting from the network appears to allow me to get back in there and delete the NAS HDD.
My unit is the "international" version (I'm from Australia) and was bought from ebay.
from:
DS-7608NI-I2 / 8P
V3.4.93 build 170408
to:
DS-7608NI-I2 / 8P
V4.1.70 build 181114
Before:

I downloaded:
NVR_K51_BL_ML_STD_V4.1.70_181114.zip
From:
DOWNLOAD EU PORTAL
I did the upgrade locally on the NVR with a monitor connected. Unzipped the downloaded file to a USB, insert USB to NVR and did the upgrade via the GUI.
Seemed to work OK, upgraded normally.
After:

So far so good, logged in via web OK, settings seem to have been retained. I'll update the thread with any issues as I bring up the cameras and attempt to get it back operational.
Update 1:
Cameras added OK
Some settings (schedules for motion/line crossing detection) were lost
I tried adding a "NAS HDD", which has never worked for me - part of doing the upgrade was to fix this, looks like it's worse. After I add a NAS HDD (FreeNAS NFS share), I get HDD Exception, unit beeps and enters a boot loop of constant restarts. Disconnecting from the network appears to allow me to get back in there and delete the NAS HDD.
Last edited: