While older versions of Nikto used the -update option, as of version 2.1.6 the git tool should be used to update (and install) Nikto. Most operating systems have an installer or package for git, and many programs with UI functionality also exist.

git pull

Every attempt is made by the maintainers to ensure that the git master branch is stable and working properly at all times. If and when major changes are planned, this work will be performed in a new branch to prevent breaking current users and installations.