Q: What is the proper way to resize a bootcamp partition?

So, i've used the method where you go into disk utility and everything, but that ended up screwing up my bootcamp partition, and I eneded up reinstalling bootcamp totally. Really dont want to go through that, so does anyone know the 'proper' way to resize a bootcamp partition. Also, I heard you have to do it through bootcamp assistant, but I couldn't find how.