The act of making an alteration or modification is an adjustment. If you buy a new pair of jeans, but they are too long, you can make a quick adjustment and hem them, have someone else hem them, or use safety pins.
The process of adapting to your environmental conditions is also called an adjustment. After you leave home for college, both you and your parents will have a period of adjustment. Some people adjust easier to change than others — you may be having a ball going to class, eating cereal for dinner, and making new friends but an adjustment your parents will have to make is that they will need to stop worrying about you.