The non-revolution guide to democracy (which may involve bankruptcy)
*Note this will raise militancy by quite a lot.
1) If you're a monarchy, set voting rights to suffrage. You'll become a Con. Mon.
2) If you're a Con. Mon, set voting rights to suffrage (if they're not already) and manually put the Anarcho-Liberal party in power. You'll become a Pres. Dictatorship.
3) As a Pres. Dictatorship, set parties to right to ban and voting rights to suffrage (if they're not already). You'll gain a 2 party system without becoming a democracy.
4) Manually set your party to your choice between the Liberal and Conservative parties. THEN grant free parties. You'll become a democracy and stay that way. At least until the election. If the Anarcho-Liberals win an election, you'll become a Pres. Dictatorship again, so make sure to do whatever it takes to drop your militancy. Zero taxes, social reforms, whatever.
If you start as a Monarchy you can get all this done as early as May 1, 1836. If you're something else, sooner.