There are many ways to edit an article after it has been published.
Click on the left-side meatball menu [...] and select Edit Article:
On your My articles screen you can edit published articles by clicking on the pencil icon next to each article:
This screen can be reached by either clicking on the top-right profile icon and selecting My articles, or by clicking on the x articles published link under your profile on the front page.
To update your content, first unpublish your blog post using the Unpublish button on the edit page. This will unpublish your article and mark it as a draft. Following this step, you can make the necessary changes. After making changes, you can republish your article or save it as a draft.
If you want to edit an article that you have previously saved as a draft, simply click on Drafts in the My Articles section and then click the pencil icon.