Necessary complexity — that which is meaningful and relevant to the task at hand — is useful and should therefore never be eliminated or even reduced. Instead, it should be managed.
When presenting information, we manage complexity by finding the simplest possible way to display it, never crossing the threshold into over-simplification. This can often be done by breaking the information down into logical and meaningful parts and presenting each part separately at first. Once your audience is comfortable with the parts, then you can combine them, perhaps one at a time, to build up to the full level of complexity in a way that people can absorb without ever being overwhelmed. Sometimes we can manage the complexity of a wealth of information by the way we organize it. For example, several concepts and facts that relate to one another can be organized on the page or screen in a way that makes the nature of the relationships clear.