My Mac is operating on OS Yosemite - can I get this updated?

Back up your data, check your applications for compatibility, click here, and depending on which iMac model you have, then on the download link for High Sierra, Mojave, Catalina, Big Sur, or Monterey.

Catalina and newer won't run 32-bit software; download and use Go64 as well as using the first link above.

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That will depend on the model / year of Mac you have. You can find it in Apple Menu->About This Mac

Post it here, and we can tell you if it can update and what macOs version it can update to.