You can update the title and description by modifying the Gadget XML file for your app: http://developer.yahoo.com/yap/guide/gadgets-xml-config.html

It seems it doesn't update the preview even if you already changed the xml from your site. I clicked the update a couple of times and tried importing the xml file (located on my server) but the changes doesn't reflect? Does it take time to reflect?

I agree, it seems to be rigid once set. I know I can change it with the gadget file, but it seems to be set. Lesson learned really