Open the song in Audacity. When the file opens a visual overview of the song will appear.
Zoom in by clicking the magnifying glass button with a + sign on it so that you can edit precise syllables.
Listen to the song while watching the overview, until you hear the word or words that you want to edit.
Click to the beginning of where the profane sound wave starts (this might take a couple listens to pinpoint exactly) and highlight the word by dragging your mouse to the right.
Open the "Effect" toolbar and click "reverse." This will reverse the portion of the song that you highlighted, making the word indecipherable.