UPDATE
UPDATE table_name SET column_1 = 値1, column_2 = 値2, … WHERE 条件式;
update users set name = 'Yamada', age = 25 where id = 1;
参考：
データの更新 (UPDATE 文) | SQLite入門 (www.dbonline.jp)
SQLite3 でデータを更新：UPDATE | GRAYCODE PHPプログラミング
Learn SQLite UPDATE Statement with Examples | SQLite Tutorial
SQLite UPDATE Query | Tutorials Point
sql – UPDATE syntax in SQLite – Stack Overflow
NULL 値に更新する
update users set name = 'Tanaka', age = null where id = 2;
参考：
in sqlite, how to update a column to null conditionally – Stack Overflow