You can't. It's something you develop while young. People claim that you increase it but they are lying. You cannot increase your IQ as you get older.
When I was a kid, my mother told me that the best way to get a high IQ is to read a lot of books. So I
advise you to read at
least one per week, and you will surely see a change. You can also practise brain games or learn how
to play an instrument.