how do i update my mac from mac OS 10.12.6 to 10.13

Backup and clone the working boot disk or whatever boot disk to an external volume and verify you can boot to it. Just in case you do not get stranded without a boot volume.

Then download High Sierra and make a macOS install thumb drive from it:

How to download and install macOS - Apple Support

Create a bootable installer for macOS - Apple Support

Or Option-Command-R boot into Internet Recovery mode and use this workaround to install High Sierra:

https://mrmacintosh.com/how-to-fix-the-recovery-server-could-not-be-contacted-error-high-sierra-recovery-is-still-online-but-broken/