Using an application like Notepad++
Use Regular Expression mode. You will search for a carriage return (Windows uses \r\n as a carriage return), some text, and then another carriage return. The replace with will give you back only the stuff in the parenthesis. Make sure you run “Replace all” as I did not test on replacing one at a time.
Find what: (\r\n.*)\r\n Replace with: \1