i tried to update to the most recent macOS that my mac can take which is high sierra. When i tried the installer it came up with the message "This copy of the install macOS High Sierra application is damaged, and can't be used to install macOS "

When you go to the App Store High Sierra page, does it say Open if so the App Store has detected there is a copy of High Sierra somewhere on your Mac. First look in your Applications folder for Install macOS High Sierra.app, if this is 5.23GBs then that is the full installer, double-clicking on this will start the installation procedure. If it is a partial download then move it to the Trash, then empty the Trash. Restart your Mac and go to the App Store High Sierra page and try downloading again. Use a cabled connection to your router instead of WiFi.