How do you prepare for a 5k (or less) run?

Question

i have been running 4 times a week, an hour each time for the past couple of weeks. Now I would like to take part in a run thas 5k or less (10k might be too much.) around august and/or september in order to set myself a goal that is achievable. However, I have no idea how to prepare myself for it. do i have to eat differently?(like cutting out choclate out of my diet or anything fatty? do i just go running like i normally do?? or do i go running for a more than an hour? do i need more than 2 months to prepare for a 5k run?

mucho thanks.!