First make sure that your footnotes are styled with Footnote paragraph style: put the cursor in a footnote and look at the leftmost toolbar dropdown menu. If it doesn’t display Footnote, force it.
If you have Footnote, display the style side pane if not already visible with F11 (on MacOS, Styles>Manage Styles or Format>Manage Styles with 6.x).
Right-click on Footnote and Modify. Go to Font tab and adjust settings.
If the modification is not effective, you have direct formatting in your notes. Select the text one note after the other and Ctrl+M.
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