$('#dialog_title_span').text("new dialog title");
$(yourElement).html("New text");
//sets yourElement innerHTML to "New text"
var text = $(yourElement).html();
//html() returns the text inside yourElement if you pass no parameters
.text("new text")
// (Note: this will change text in all H1 Elements)
$('h1').text("good bye");
$('#element').text('set text here!');