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.
How do you get a high iq?
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.