Pro tip to Apple: Perhaps don’t make a watch whose one of the primary feature is to be used at night, and then expect everyone to charge it during the night. You can’t both track sleep and charge, it is an either or situation.

As far as I can tell you must be a quite advanced user to install updates outside the «while charging during the night» schedule.

Firstly you must navigate deep into the settings. But not only that, you can’t do this while wearing it, as if you update without charging it always fails.