Hello Hamed,
This is not a Gnokii question, it is a question to ask of the people
that made your Linux distribution.
For example, if you were on Red Hat, one might assume a program can be
removed with the "rpm" program
Another example, if you were on Debian, one could also assume a program
can be removed with the "apt-get" program
Of course, if you installed it from source, you will have to remove it
yourself manually.
In other words, you need to know more about Linux - especially the
flavour of linux you are using.