I also want to know how

It's a bit complicated, but you have to go against Terra and win the civil war. After about a month, you'll get an election event, you must choose Luis Batlle Berres. You must also appoint as advisor Andres Martinez Trueba. Once you have those two, you select the decision "Undermine Berres", and from there a chain reaction of events will occur until you get a collapsed government. From there, you can go anarchist.