I have found a great way I think to upgrade BE releases.
Say I am running BE at abc.com and wish to upgrade and not experience any downtime issues.
In my hosters control panel I create a sub domain called bcd.com and a website with the same name.
I then install to a clean folder the latest BE release, copy over the app.data and themes folders using the control panel file manager which is faster then uploading,
Do any css or master page tweaking if using a new theme.
When I have it running without any issues go in your control panel and point abc.com to bcd.com and all is well.
Then when a new release comes along that you wish to upgrade to, delete all the files in the abc.com website and repeat the process and then point bcd.com to abc.com.
Then wait for the next release, this way you only upgrade and make the switch when all is working the way you want, sometimes it may be working great locally but then run into issues on the server.
What do you think?