tell me the best way to update dictionary key value?

As you said the order was important I think the easiest way is to re-create the dictionary, not very efficient for larger datasets though.

We can iterate db to re-create it, the only thing we need to look at is whether to use the key from user or db. If the key exists inside user_values then we can fetch it’s index and use that to get key from user_keys, otherwise we use key.

user = {'school': ['books', 'pencils', 'sheets', 'notebooks']}
db = {'education': ['books', 'pencils','sheets','notebooks'],
      'actors': ['student','teacher','principal']}

user_keys = tuple(user.keys())
user_values = tuple(user.values())

new_db = {user_keys[user_values.index(value)] if value in user_values else key: value for key, value in db.items()}

>>> {'school': ['books', 'pencils', 'sheets', 'notebooks'],
     'actors': ['student', 'teacher', 'principal']}