This VIDEO showing how to correctly update and upgrade your existing EVE VM to the newest version.

Shortly:

Connect to your EVE server on CLI as root and type following commands: ( update from V76 to V77 )

apt-get update

apt-get upgrade

 

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SPECIAL NOTES: ( update from V71 or lower  to V2.0.3-77 )

Stop all labs

Use the command :

/opt/unetlab/wrappers/unl_wrapper -a stopall
apt-get update
apt-get dist-upgrade

Finally reboot server