To Remove an Item from "New" Context Menu

1. Open Registry editor [by typing regedit in RUN dialog box and press Enter]. 
2. Now expand "HKEY_CLASSES_ROOT" key.
3. Search for the file type you  want to remove from "New" menu, e.g. for removing "Rich Text Document (.rtf)" file type look for .rtf key under HKEY_CLASSES_ROOT key.
4. Now Expand it and delete the ShellNew key present under it.
5. That's it. The file type will no longer be available under the "New" menu.