Hi,

I want to rename the menu items and its content in orchard dashboard page. Can you please let me know where i have to change this?

The only way is to edit the source, which I don't really recommend, but if you are that desperate...

To change, for example, Comments to Discussions you would go to Orchard.Comments and open the file AdminMenu.cs and change it there. 

But don't do it, someone somewhere will cry!

You mean the dashboard you see first when you access the admin section? Have you looked at the gallery? http://gallery.orchardproject.net/List/Modules/Orchard.Module.Orchard.Contrib.Dashboard