To check your current version issue the following command:

$ ntk sys version

If version is 4.2.xx you can update automatically, you just need to get newer cli tools: 

$ docker pull notakey/cfg:4.2.32   
$ ntk cfg set cli.image notakey/cfg:4.2.32   
$ ntk cli update_wrapper
$ ntk sys update

If version is 4.1.xx or older, you have to upgrade your appliance. See Notakey Authentication Server documentation for upgrade instructions.