Get your journalist to follow you. Take them up to a bookshelf and tell them to "Use". Repeat this many times. Eventually you will have increase their Intelligence. This also works with everyone in the game.

Just like how you can raise your photographers and writers intellect by making them follow you and telling them to use bookshelves, you can also do for Hef. His intelligence will also rise, but it sometimes will not work for the different
bookshelves.

Enter to the upstairs office with a writer. Make them write an article about anything using the desk. This will increase their Intelligence. If you have purchased the better desk, it will increase faster. Note: Remain with them while
they are writing the article.