Untitled

<!DOCTYPE html>
<html>
<body>

<p>Click the button to replace "Microsoft" with "W3Schools" in the paragraph below:</p>

<p id="demo">Żużlowcy Apatora Toruń</p>

<button onclick="zamiana(document.getElementById('demo').innerHTML)">Try it</button>

<script>
function zamiana(u) {
    var str = document.getElementById("demo").innerHTML;
    var res = str.replace(/ż/gi, 'rz');
    document.getElementById("demo").innerHTML = res;
}
</script>

</body>
</html>