You can "promote" a paragraph by clicking inside it and then pressing Alt+Shift+Left arrow. I doubt that you could do this in a simple step (that is, it won't necessarily work as expected if you select all the text and promote it).

Note that managing multilevel lists will be a lot easier if you set them up with paragraph styles (one style per numbering level). See the article at https://shaunakelly.com/word/numbering/numbering20072010.html.

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Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional