The people at the polling station then write down your voting card number on each envelope for you, and post the voting envelopes (which have a small opening showing the colour of the voting slip) in each of the ballot boxes for the national, regional and municipal election. If you decide that you want to vote for a different party, all you need to do is turn up at the polling station where you are registered with your voting card and vote a second time for the party you now want to vote for. This is because your voting card has a unique number (which is different from your personal number to keep each vote anonymous), and each unique voting card number can only have one vote connected to it.