I want to change the blog layout.I want to order this in title then publish date,picture and then description.but I don't know how to do this.can you help me plaese?
Please read up on some Orchard documentation about placement, alternates and shapetracing.
The simplest thing you can do, for just changing the order of rendering, is changing the placement.info of your theme to something like this:
<Match ContentType="Blog">
<Place Parts_Title="Content:1" />
<Place Parts_MetaData="Content:2" />
<Place Fields_MediaLibraryPicker="Content:3" />
<Place Parts_Blogs_Blog_Description="Content:4" />
</Match>
If you want to have full control over the rendering of the layout you can create an alternate. Use the shape tracer to find the correct alternate (probably something like Content-Blog.cshtml), and tweak your stuff in there.