You must have ESXi shell access and all of these commands must be executed on the ESXi host.
Make sure you have proper internet connection on the ESXi host.
Before proceed with the upgrade, you must shutdown ALL VMs and enable host maintenance mode. When done, make sure to exit from host maintenance mode.
1.1. Access ESXi console and verify configurations such as DNS.
1.2. Get a list of all registered virtual machines and notedown its VMIDs.
1.3. Get the current state of a virtual machine by running the following command.
1.4. Shutdown ALL virtual machines using VMIDs.
1.5. If a virtual machine fails to shut down gracefully, power it off.
1.6. When the ALL VMs are in shutdown state, enable host maintenance mode. If this is failing make sure that there are no running VMs on the ESXi host.
2.1. Allow HTTP traffic through the firewall.
2.2. Check VMware online depot for ESXi 6.7 profiles.
2.3. Upgrade to the latest ESXi version.
2.4. Revoke HTTP access through the firewall.
2.5. Exit from host maintenance mode.
2.6. Reboot the server
Once the ESXi host is rebooted, please make sure to power on VMs if it is not configured to power on automatically.