Modified SharePoint Site Title Using JavaScript Code

Edit SharePoint Page and insert the script editor:

<script language="javascript" type="text/javascript">
    //Ensure the Client Object Model is ready before you use it
    ExecuteOrDelayUntilScriptLoaded(GetTitle, "sp.js");

    function btnUpdate_onclick()
    {
        //Update the site's Title property
        site.set_title(document.getElementById("txtbutton").value);
        // site.update();
        site.update();
        // addd the site to Query queue
        context.load(site);
        //Run the Query on the server
        context.executeQueryAsync(onTitleUpdate, onQueryFailed);
    }

    function onTitleUpdate()
    {
        alert('Title has been updated');
        //Refresh the page
        SP.UI.ModalDialog.RefreshPage(SP.UI.DialogResult.OK);
    }
    var site;
    var context;

    function GetTitle()
    {
        //Get the current client context
        context = SP.ClientContext.get_current();
        //Add the site to query queue
        site = context.get_web();
        context.load(site);
        //Run the query on the server
        context.executeQueryAsync(onQuerySucceeded, onQueryFailed);
    }

    function onQueryFailed(sender, args)
    {
        alert('Request failed' + args.get_message() + '\n' + ar.get_stackTrace());
    }

    function onQuerySucceeded(sender, args)
    {
        document.getElementById("txtbutton").value = site.get_title();
    }
    // ]]>
</script>
<p>
    <input id="txtbutton" type="text" />
</p>
<p>
    <input id="Button1" type="button" value="button" onclick="return btnUpdate_onclick()" />
</p>