There are three approaches to correcting a published article, depending on the impact of the correction.
Corrections to spelling or simple grammar (a change in punctuation, etc.) should simply be made.
Corrections that change the wording of the article should be made inline, with a "Corrections" section added at the end of the article outlining the date and the change made. This should be done only if absolutely necessary.
A clarification or explanation of the text should be made in the "Corrections" section, with a note added to the original text to "See Correction", linked to the explanation/clarification. See, for example, We Love Open Source Software. No, You Can’t Have Our Code (Issue 5).