Amazing! The install file and the web site said it would be painless – and indeed it was painless!
I downloaded 4.5.2, looked at it, and it seemed to touch EVERYTHING in the system. That got me quite scared, of course, and frankly I quite didn’t buy the fact that every file needed to be changed because of ‘copyright notices’ and such. But in the end I trusted the ease of getting my old site back, if needed, and I risked it.