im trying to upgrade my Mac OS Sierra from version 10.12.6 to a 10.14 but its says no update found

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. Make sure to use Only Safari to commence the download as Others may not work

Make a Time Machine Backup Before attempting. Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers.

Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation

An update is a newer version of the currently installed operating system. That message means that you are up to date. You need to learn the difference between an update and an upgrade which is the installation of a newer operating system. Upgrades can be found in the Apple App store. They are completely different things.