To edit, put your cursor into any field.
To change the casing of the title, right click in the Title field, and transform the text to the appropriate casing.
If you have a citation that just won't format correctly, and you don't want to spend a lot of time fiddling with it in Zotero, you can edit it in Word. Be aware that this will break the link for that one citation, and it can't be updated in Zotero anymore.
Sometimes it's a headache trying to get Zotero to format citations as you want them to display. A workaround is to edit the citation in Word instead of in Zotero. Please be aware that:
For Chicago Notes/Bibliography style, choosing the correct Item Type will help Zotero format it correctly.
For more tips, see the PDF below.
For these source types, use the BOOK Item Type:
For these source types, use the REPORT Item Type: