'descendant::Windows[Title ='What's new and improved in SharePoint 2013 : Customizing the interface']' has an invalid token.
On the Home page of your site, click the Settings button (the small gear icon next to the name of the logged-on user). On the menu that appears, click Site Settings.
On the Site Settings page, in the Look And Feel section, click the Change The Look link.
On the Change The Look page, click one of the displayed templates.
On the Change The Look page for the template you have selected, choose a different color scheme for the template, if you want.
Select a non-default site layout for the template, if you want.
Select a non-default font for the template, if you want.
Click Try It Out.
Click Yes, Keep It to save your changes.