Question

Iv'e seen it. But don't know how

Answer 1

There is no such thing as IV training. IV's are set once the Pokemon is gotten. So IV's cannot change or be trained once the Pokemon are obtained. Youre probably confused with EV training. If you are here is a page teaching you how to EV train. The page is long but EV training is complicated so if you really want to know just read this: http://www.gamefaqs.com/ds/960099-pokemon-heartgold-version/faqs/59369