Log in as 'Wizard' in your Online Family Tree (GeneWeb), then click 'Edit Places' in the left sidebar:

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This will open a new page with the full list of the places which are cited in your family tree:

EN-edit-places-01.jpg

Click 'Update', edit the place name, then click 'OK' to automatically update it in your entire family tree:

EN-edit-places-01.jpg