how to upgrade from Ventura to sequoia

Here is a list of hardware requirements for macOS 15.x Sequoia......does your Mac meet those requirement?

macOS Sequoia is compatible with these computers - Apple Support

If so, then go into System Settings--->General--->Software Update. You should see an option to install/upgrade to Sequoia if your hardware is compatible.

If your hardware is not compatible, then you will need to buy a new Mac, or perhaps you will need to use some other third party software which still supports Ventura.

FYI, you can get the exact model of your Mac by clicking the Apple menu and selecting "About This Mac". You should always provide the exact model of your device when asking for assistance online since it is usually required for many support issues.

Check System Settings > Software Update. If nothing is listed, your Mac is too old for Sequoia.

Update macOS on Mac - Apple Support

In theory, running this Terminal command will list ALL Software upGrades the computer Qualifies to run

 softwareupdate -l