how do I update mac os 10.13 to the latest, 13.2 I think?

Back up your data, check the application compatibility table, click here, and then on the download link for a more-recent OS. That model's maximum one is Monterey.

Catalina and higher won't run 32-bit software; if you upgrade to one of them, use Go64 as well.

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What year model is your iMac?

see > Identify your iMac model - Apple Support

+1 Niel beat me to the punch.