Does changing DNS improve internet speed? Which DNS should I use in Sydney?

DNS doesn't change your raw download speed, but it does affect how quickly websites start loading (domain resolution time) and can affect access to certain content. Good options: Cloudflare (1.1.1.1) — generally fastest and privacy-focused; Google (8.8.8.8) — reliable and widely used; Quad9 (9.9.9.9) — blocks known malicious domains. Change it in your router's DNS settings or your device's network adapter settings.