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.

How to Add Items to “New” Context Menu in Windows

1. Type regedit in RUN dialog box and press Enter. It'll open Registry Editor. 
2. Now expand "HKEY_CLASSES_ROOT" key.
3. Now look for a sub-key having same name as the file type which you want to add in "New" menu. e.g. if you want to add JS file type to "New" menu, look for .js key under HKEY_CLASSES_ROOT key.
4. Now right-click on it and select "New -> Key" option. It'll create a new key, give it name ShellNew
5. Now in right-side pane, right-click and select "New -> String Value". Give it a name NullFile and press Enter.
6. Hurray!! You  done it. Now you will have a new JavaScript file option in context menu.