Do I have to change the article name when it is the extended version of my published paper? I'm submitting the extended version of my published conference paper to a journal that has a special issue specifically related to that conference.
Besides adding 30% of more material to the article (as the computer science routine), do I have to change the article name?

On one hand, everything is the same besides having more experiments and more formulations or extra explanations, and it is obvious that the article and the paper are the same works.
on the other hand, how people may decide to cite which one later on?
Usually, there is no formal requirement that the title has to be changed. In fact, if the journal paper is just the long version of the conference paper, I would recommend not to change it, so that the connection between the two papers is obvious to people who see the paper in a list of references.

As soon as the journal version of the paper has appeared, it is generally assumed that this is the version that should be read and cited, rather than the shorter conference version. By keeping the title unchanged, you tell readers that there is no need to read the earlier one as well.