In infobox: add Template:death date and age to parameter death_date; replace Template:birth date and age with Template:birth date.
In lead sentence, change (born birthdate) to (birthdate – deathdate).
In body: in appropriate location, add information about the death and a reliable source; change the tense of verbs to past.
In categories, add the appropriate year of death category, such as Category:2020 deaths.
On the article talk page, in the WPBiography project template, change living=yes to living=no.