The concept of "killing" in inapplicable to those plug-ins. This is not an installed service taking up some amount of memory, or something like that. Javascript is based on automatic memory management. If some object eventually becomes inaccessible, the host will eventually reclaim the memory.
If you mean something else, such as removing some element from the page, ask about it. But generally, it's nothing more than removing some element from HTML DOM. With jQuery, this is all described here:
http://api.jquery.com/category/manipulation[
^],
http://api.jquery.com/category/manipulation/dom-removal/[
^].
—SA