How can I update from 10.13.6 to 10.14?

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 Other may not work

Make a Time Machine Backup Before attempting. Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina and Big Sur Only support 64 bit and there is not workaround.

Are there any AntiVirus, Disk Cleaner, Optimizers, Defrag, VPNs 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.

How to Upgrade to  macOS Mojave:

❗️- Backup your data! - (You’ve been warned.)

Learn How to Back up your Mac with Time Machine:

https://support.apple.com/en-us/HT201250

❓- Is your Mac compatible with macOS 10.14 Mojave? 

That depends on the age of your Mac. Check the requirements here:

macOS Mojave - Tech Specs - Apple Support

These Mac models are compatible with macOS Mojave:

• MacBook (Early 2015 or newer)

• MacBook Air (Mid 2012 or newer)

• MacBook Pro (Mid 2012 or newer)

• Mac mini (Late 2012 or newer)

• iMac (Late 2012 or newer)

• iMac Pro (2017)

• Mac Pro (Late 2013; Mid 2010 and Mid 2012 models with a

recommended Metal-capable graphics cards.

For details about your Mac model, click the Apple  icon at the top left of your screen and choose About This Mac. 

✅ - Download the macOS Mojave upgrade installer here:

https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12

(Don’t use FireFox for this link)

How to get old versions of macOS - Apple Support

Welcome and thank you too :-)