Slow Install on Windows 10

Norton Internet Security (Xfinity) is taking tens of hours to install an update, following an OS update from Windows 7 to Windows 10.  Any suggestions for speeding it up?

This is on a small netbook (Atom CPU with 2 GB RAM) so expected to be slow.  But it's been running for 12 hours now and the completion bar is 80% across and creeping like a tree sloth.

It has an SSD so that's not a factor.  Norton 360 is using about 25% - 40% of the CPU, according to Task Manager.

The reinstall was Norton's idea; it popped up shortly after getting the machine up on Windows 10.