2. Right click on the project -> properties -> Silverlight rename the same as you give first on the red marking only.
3. Click on assembly also rename here only marking
4. Buid the project. if you run it you will get error. becoz the aspx file now running the previous xap file.
so you must also have to rename as your newly assembly file/xap file in the aspx file as following figure.
Now build & run you application.