If you want to change chart titles and labels you should use data plot custom attributes to parametrize them and then use setPlotCustomAttribute(attributeName, attributeValue) or view_setPlotCustomAttribute(viewId, attributeName, attributeValue) to update attributes and, thus, update the text fields.
Note: Refresh() or View_Refresh(viewId) method should be called to apply the changes made.
The sample below allows you to update chart title and footer.
View XML: Open XML File with data plot custom attributes.
Code used to update looks like that:
var title = document.getElementById("title").value;
var footer = document.getElementById("footer").value;
chart.setPlotCustomAttribute("title", title);
chart.setPlotCustomAttribute("footer", footer);
chart.refresh();
Title:
Footer: