2010 asp.net change file name

Question

I have a C# 2010 web form application that uses linq to sql connections. I am having problems with the visual studio.net 2010 ide opening up very slowly.
The problem looks like I need to change part of the name for a dbml file. Here are the names I am working with;
1. testapp.dbml,
2. testapp.dbml.layout, and

3. testapp1.designer.cs.


I know the problem is the name called testapp1.designer.cs.

I do not know how to change the name of this element. The visual studio.net ide will not let me change
the name from  testapp1.designer.cs to testapp.designer.cs.

Thus can you tell me how to change the name?

If you think something else is causing the problem, can you let me know what it is and how to solve the problem?