How to edit diagram

So I posted a diagram, and would now like to edit it. How would I do this?

Edit the post where it is, click it, click the diagram so that it is selected and then click the Insert Chess Game or Diagram toolbar option.

Short and precise ...

Another option is - if you do not want to edit, but also copy it, and put it for example into an newer comment: go to the sign that looks similar like this "<" (with points at the ends) below the dia, click on it, click on the left tab on top (download symbol, looks like an arrow pointing into a trough), then the PGN data is opened, copy that, make a new comment with a new dia, and upload this PGN data there, continue with "setup game" (for example to flip board) as usual, edit moves as usual ...

I've always wondered how to do this.  I've been posting analysis diagrams, static diagrams and puzzles for years and never bothered to learn how to edit them.  Hard to believe I know.  Anyway I typed "edit diagram" in the search box and this thread came up first, and it was exactly what I needed.  Simple process too.

Thanks.