how to upgraded the High Sierra OS to Monterey 12.7

First, check whether your Mac is compatible with Monterey.

macOS Monterey is compatible with these computers - Apple Support

If it is, use Safari and the App Store link for Monterey in this Support document.

How to download and install macOS - Apple Support

Note that if you upgrade to Catalina or later (including Monterey),

• 32-bit applications will stop working
• iTunes will go away in favor of separate apps: What happened to iTunes? - Apple Support

The Age of this computer will Govern what newer version of macOS it will Qualify to install. 

Use About this Mac from the Apple Icon on Desktop - the required Information will be there.

With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install.  For Best results use Safari to commence the download as Others may not work.

Safari will open a redirect and open the Apple Store where the download can commence.

Does this computer appear as Listed and qualifying for an upGrade to a newer version of macOS ? 

If Yes, suggest having at least 50 GB of Empty Space on the drive.

It will allow the Full Version ( about 12.xx GB ) to download, expand and then commence to install.

If there is Third Party Security Software installed - remove it.

It will interfere with both the download and installation process.

The below links will help identify which version of macOS  this computer may Qualify to run.

Computer Qualify for the Monterey upgrade

macOS Big Sur 11 hardware requirements

macOS Catalina 10.15 hardware requirements

Make Time Machine Backup  before doing any upGrades