Greasemonkey: Either right-click the Greasemonkey status bar icon or use the Tools menu to open Manage User Scripts. Select the userscript you wish to change and click Edit. Follow the instructions at the beginning of the file. Save the file and close Wordpad.
Note about Greasemonkey: The first time you click Edit you will be prompted for a text editor. I recommend using Wordpad. If you have already selected an editor other than Wordpad, type "about:config" in the address bar, press enter, then search for "greasemonkey.editor". Right-click the entry and select "Reset". You will be prompted for Wordpad's location the next time you press Edit in Manage User Scripts.
Trixie: Open the Trixie Options from the Tools menu and select the userscript you wish to change. Click the View button. Follow the instructions at the beginning of the file. Save the file and close Wordpad.
Turnabout Advanced: Open the Turnabout Options from the Tools menu and select the the userscript you wish to change. Click the Edit script button. Follow the instructions at the beginning of the file. Save the file and close Notepad.