Update app in the marketplace wp7

Question

I have been trying for 3 hours to update a new .xap for my current app.

Can you please give me some intructions:

I have read a lot of posts and I didn't find anything:

http://msdn.microsoft.com/en-us/library/hh546830(v=vs.92).aspx

http://msdn.microsoft.com/en-us/library/gg442301(v=vs.92).aspx

I always get this error message:

This application name is already in use or one of your other apps

Thanks in advance.