hi
They choose themselves either through political revolution or military coup.
The dictator--one supreme leader who answers to no one but himself.
a socialist leader is chosen by the citizens in a democratic election.
the leader of the Netherlands is chosen by voting or the person is in the parliament.
This partly depends on what you mean by a dictatorship and what you mean by "have Islam as a religion". Parade magazine publish a list of dictatorships; countries with an authoritarian leader with no legal ways of replacement. Of the top twenty dictatorships, nine could be said to be largely Islamic, so based on this most dictatorships are not Islamic.
The dictator (leader) can force the people to do hatever he or she wants. Example: Adolf Hitler was a dictator.
How leaders are chosen in denmark
the leader who the other leader has chosen is the new leader
Peter was chosen as the leader of the Church and apostles. Pope Gregory was chosen to be the pope and leader of the Church.
voting
By elections
They are chosen by people voting every 2 years.