How to make it default

If you're using a 64 bit version of Windows, then the Program Files folder is for 64 bit apps and the Program Files (x86) folder is for 32 bit apps.

'x86' is a term which is generally used nowadays to signify 32 bit Intel-compatible processors though, technically, it goes right back to the original Intel 8086 which was a 16 bit processor.

'x64' is generally used to signify Intel-compatible 64 bit processors though, for some reason, MS chose not to use it with the Program files folder.

What is the reason for having (x86)
Program Files (x86)

I don't know for sure but my guess is that it wouldn't want to change the 'VS Express for Desktop' start menu shortcut automatically if VS 2012 Express for Windows Desktop is still installed on your machine.

If you're using Windows 8, there might also be some issues with that.

OK it is working now. Reason it didn't work before is there is a white space between \ and Common7 I removed it.

"C:\Program Files (x86)\Microsoft Visual Studio 12.0\ Common7\IDE\WDExpress.exe"

Thank you for your help.

Can you tell please why VS 2013 Express program is not in my start menu?

Well, that's the folder for storing your projects etc.

What you need is the folder which contains the VS Express 2013 for Windows Desktop executable (WDExpress.exe or whatever it's called) and its support files.

Using Windows Explorer or the command line, I'd see if you can navigate to:

C:\Program Files (x86)\Microsoft Visual Studio 12.0\ Common7\IDE

and check whether it's in there.

I have Visual Studio 2013 folders but I couldn't find out way to install it, therefore I went to external website to download. I attach the content of the VS 2013 folder in my system.

Problem is from the above link I downloaded VS 2013 and install it, but I couldn't see any addition of VS 2013 in my start up menu. In other words VS 2013 is not retained by my system I don't why. But VS 2012 Express is in my start up menu. 

I've just tried that link but VS 2013 Express for Windows Desktop is definitely there. Just click on the name to get the download link.

I'm a bit puzzled though as I thought you'd already downloaded and installed this on your machine?

I couldn't find out the spaces in the file path.

In the following website there is Visual Studio Express 2013 for Windows Desktop, but there is no download available. Please tell me the reason.

http://www.visualstudio.com/en-us/downloads#d

Do you know any authentic site where I can download Visual Studio Express 2013 for Windows Desktop?

Well, the first one certainly won't work but the second one should work if the directory structure for VS 2013 Express is similar to that of VS 2012 for Windows Desktop whose default location is:

"C:\Program Files (x86)\Microsoft Visual Studio 11.0\ Common7\IDE\WDExpress.exe"

Notice that there are some spaces in the file path so the whole thing should be surrounded with quotes when pasting it in to the Target box.

If you're not doing this, then it might explain the error you're getting.

Target property for "Express 2012 for Windows Desktop" is as follows

"C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\WDExpress.exe"

When I pasted following two, error messages are coming. I attach the error message as well.

"C:\Program Files (x86)\Microsoft Visual Studio 12.0"

"C:\Program Files (x86)\Microsoft Visual Studio 12.0\ Common7\IDE\WDExpress.exe"

You'll need to change the Target property so that it points to VS 2013 rather than VS 2012 Express for Desktop.

If you right the click the entry for VS Express for Desktop on the Start menu and choose Properties, you should see the Target property under the Shortcut tab.

As I don't have VS 2013 Express for Desktop I don't know what the default path is but, if you have another entry for it under the Start menu, you should be able to copy it from there.

I googled it but could only find out that the path begins with this:

C:\Program Files (x86)\Microsoft Visual Studio 12.0

Whenever I open "VS Express for Desktop" it is default to "Express 2012 for Windows Desktop".

How to make it "Express 2013 for Windows Desktop"?.

I have "Visual Studio 2013" folder in my system.

Please help me.

I try to install "Visual Studio 2013" from other site but it didn't work. 

If i understand your question right then this link : http://msdn.microsoft.com/en-us/library/aa991992.aspx might help u.