So tell him to accept the update, the leave the box alone, if it appears to be hung, leave it for half an hour ( should be enough time for update to run - unless you on slow line or update server is dead slow ), then he can do the pull power plug, re-insert after an interval and update continues.
Otherwise he just keeps on not accepting update, till it happens when you are there.
No simple solution for the elderly and technically inept. Maybe wait an hour after it hangs, if it does, will be better, as then you are not likely to brick it halfway through the update.
Difficult