How to become an exchange student?

I want to become an exchange student and study in Ireland, but i don't know how, so any information would be appreciated.How to become an exchange student?I am not sure how to do it during the school year but there is a program called People to People or maybe national ambassadors association. It last around 20 days and you go to several different countries and experience a lot. It cost around $5,500 depending on what trip it is.