They're all in the UK portal here:
www.hikvisioneurope.com
You'll need to update through multiple versions. I'll post a screenshot in a moment with which ones to use....
Here you go:
View attachment 9983
That'll take a while - 8 updates. It's important that after each update, when the recorder reboots, that you delete your browser history before accessing the web interface again, otherwise you may get page not found errors (you definitely would after the first update as V3 to V4 brings huge changes to the GUI). Of course you don't have to do the updates using a browser. You could use a USB drive. If you do that you'll need to put the single, extracted 'digicap.dav' file on the root of a drive, plug it in and do the updates via the maintenance menu (you'd have to unplug the drive each time and replace the file with the next version)