upgrade to a newer OS with better security?

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

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

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When you install MacOS 10.13 High Sierra, the drive setup will be automatically adjusted for you to use Apple File System going forward. You should install that version deliberately to get the best conversion. If you try to leap directly to the endpoint, your drive may not be adequate, and that version may not be so willing to convert it for you.