How do I delete a script?

First, simply delete the text of your script from your .hss/.txt file, and reimport the file.

But don't stop there! You also need to remove any references to the script from within your game in the editor, or else you will get "script # does not exist" errors while playing the game. Just replace the script trigger with None. You can use the Find broken script triggers option in the Script Management menu to find these.