You just login as you usually do, and then click on the My Articles TAB (i.e., button.) If your article is still in the queue (meaning it hasn't been published by an editor, yet), you will see a button labeled Manage Queue.

Click that button and you will be taken to a page which lists all articles of yours in the queue. You can click on the Modify link next to your article name, and edit the article, as you usually do.

Note that it is also possible that the article may have this wording next to it: Currently Being Reviewed by an Editor.

In which case, you cannot edit it, but will soon receive a message that it has been accepted or rejected.  If accepted, you simply login and go to the My Articles section. You will see your article in that list and may then modify it (IF it is within 24 hours from the time it was approved.)