The Plugin can be installed directly from the main WordPress Plugin page.
- Go to the Plugins => Add New page.
- Enter 'correct my headings' (without quotes) in the textbox and click the 'Search Plugins' button.
- In the list of relevant Plugins click the 'Install' link for Correct My Headings on the right hand side of the page.
- Click the 'Install Now' button on the popup page.
- Click 'Activate Plugin' to finish installation.
- If your subheadings start from the H3 level go to Settings => Correct My Headings and change the default setting.