Your choices are:
1) Run Windows on your Mac via Bootcamp, Parallels, or Fusion
2) If you have a current version of Photoshop you can contact Adobe and switch your license from the PC version to a Mac version, they will give you details.
3) If you do not have a current version you can contact Adobe and they can tell you how to crossgrade from your old PC version to a new Mac version.
4) Upgrade to the Creative Cloud and run Photoshop on your Mac or PC as needed.
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