Hi,
according to this link direct dist-upgrade of Alexandria from Debian 7 to Debian 8 would not work on OpenVZ system:
http://board.nwrk.biz/viewtopic.php?id=63

So it seems to need backup, clean install of Debian 8 64bit minimal from Control Panel, and restore.

I don't start to do anything to server before I have made tests etc locally on my laptop.

I'll also notify when I plan to upgrade server.

BR,
xet7