So I recently, for the first time in my life, changed my part. It usually parts on the left side of my head and now its on the right. The reason was because I have a giant cowlick or section of hair that grows in the opposite direction of the rest on the back left of my head. I finally got sick of trying to deal with it and so the ordeal of changing my part began. So this is how I did it.
snap pins or bobby pins
hair spray or mousse
Step One: If you have bangs make sure to accommodate them with the new part. I cut mine myself, but if you need a professional then go for that. Make sure to tell them exactly where you want your new hair parted and tell them to cut your hair accordingly. This step is optional, but sometimes when changing the part it also changes your style (layers, uneven on sides or crown) so keep that in mind.
Step Two: When hair is wet comb it to your new part. Spray with heat protector and add mousse (you can skip the mousse if you only have hairspray). Then blow dry hair so when dry it stays in the position of the new part. Blow dry any opposing hair to the opposite side.
Step Three: If you are leaving your hair down (recommended) spray hair with hair spray, especially where the hairs position is being changed.
Step Four: If you are going to sleep after you have done the previous steps pin the opposing hair down to make it stay in the position you want while you're sleeping.
Basic Concept: If the hair disagrees, spray it down and pin it until it agrees.