boot manager installed windows 7 twice how to delete one?

The easiest way to remove an entry in the Windows 7 Boot Configuration is to use msconfig. 

To launch msconfig:

1.  Click Start

2.  In the Search text box, type msconfig

3.  Launch msconfig by selecting it from the search results above the search text box.

After msconfig is launched:

1.  Go to the Boot tab

2.  Select the boot entry you want to delete.

3.  Click the Delete button and then click OK.

Make sure to be logged in to the Windows 7 partition you want to keep when performing these steps so you don't delete the good installation by mistake.