[An AutoLisp file is not a script. That word has a related but different meaning in AutoCAD.]
"Unload" and "delete" are very different things.
If you really mean "delete," you can go to the folder in a file explorer and delete the file, or within AutoCAD an AutoLisp function could do it.
If you mean "unload" from the current drawing, such as to eliminate things like commands defined in the file, that is not an option for AutoLisp routines. See Help for the >APPLOAD dialog box<, under Unload/Remove: "LISP applications cannot be unloaded." But you could remove it from the Startup Suite in APPLOAD, or from being (load)ed or (autoload)ed by an acaddoc.lsp file, or from whatever else is loading it, so that it will not be loaded in other drawings subsequently, nor in the current drawing the next time it is opened.
Kent Cooper, AIA