Nikto can be automatically updated, assuming you have Internet connectivity from the host Nikto is installed on. To update to the latest plugins and databases, simply run Nikto with the -update command.
perl nikto.pl -update
The -update option cannot be abbreviated.
If updates are required, you will see a list of the files downloaded:
perl nikto.pl -update
+ Retrieving 'nikto_core.plugin'
+ Retrieving 'CHANGES.txt'
Updates may also be manually downloaded from http://www.cirt.net/