10.13.6 is the latest version of macOS High Sierra and there are no updates available.
If you need a newer macOS version, Mojave 10.14 or Catalina 10.15, then you will have to upgrade your Mac's OS, IF the Mac is compatible with a newer OS. If your Mac is not compatible with newer macOS versions, you'll have to replace the Mac with one newer, or use some alternate to Adobe software.
How to Upgrade macOS:
The macOS version you can upgrade to depends on the year your Mac was released.
Click the (Apple) menu at the top of your screen and choose About This Mac.
Check the Compatibility of your Mac with newer versions of macOS:
➡️ macOS 10.14 Mojave is compatible with the Macs listed here
➡️ macOS 10.15 Catalina is compatible with the Macs listed here
➡️ macOS 11 Big Sur is compatible with the Macs listed here
➡️ macOS 12 Monterey is compatible with the Macs listed here
❗️ – IMPORTANT – Your 32-bit apps won’t work in Catalina, Big Sur or Monterey.
https://support.apple.com/en-us/HT208436
Use the free utility Go64 to check the compatibility of your apps:
https://www.stclairsoft.com/Go64/
✅ - IF your Mac and apps are compatible, then using Safari only, download the macOS upgrade installer app:
Click > Mojave, Catalina, Big Sur or Monterey.
Once downloaded, double-click the “Install macOS…” app in the Applications folder to begin the upgrade.