If there is a particular Article you need to update, you first have to find it before you can edit it. From the main menu, select Content > Articles and you will see a list of the first 20, with options for paging progressively through the list to find the one you want. If you know a word or phrase that is in the Title, just type that into the Search field and press Enter (or click on the spyglass button). That will filter the list to those containing the search word. If you know the Category of the Article you are looking for, first click the Search Tools button, then select the appropriate Category from the drop down list. Again, this will filter the list.

When you can see the Article you want to edit, just double-click it and you will be able to edit it using the same screen as shown above.