For the most part, the easiest way to edit things in Parity Builder is to click (or possibly double-click) on them, and then just hack away at them with the mouse and keyboard. Nonetheless, in most places where you can edit, the Edit menu provides the most commonly used editing operations (cut, copy, paste and select all). Note that in the Messages and Assignments tabs text may be split among multiple panels. The panels are read-only (you cannot cut, delete or revise them), and the Select all menu option will only select the text from one panel (the one in which the cursor currently resides).
