Altering clothing can take many forms.
Taking seams in: If certain garments are too big, the seams can be taken in. This is done by trying on the garment inside out, and getting someone to pin or mark on the seams where they would fit better. Then the garment is resewn at the markings to reveal a new and improved fit to the garment.
Letting seams out: If certain garments are slightly too small, in some cases the seams can be let out. This is done by trying on the garment inside out, and getting someone to pin or mark on the seams where they would fit better. Then the garment is resewn at the markings to reveal a new and improved fit to the garment.
Raising hems: If certain garments are slightly too long in the leg for trousers or sleeves on shirts or blouses, the hems can be raised or taken up. This is done by trying on the garment inside out, and getting someone to pin or mark on the hem where it would fit better and where the new ideal length would be. Then the garment is resewn at the markings to reveal a new and improved fit to the garment.
Lowering Hems: If certain garments are slightly too short in the leg for trousers or sleeves on shirts or blouses, the hems, if big enough or with enough allowance, can be lowered slightly. This is done by unpicking the hem to see how much allowance there is, then trying on the garment inside out, and getting someone to pin or mark on the hem where it would fit better and where the new ideal length would be. Then the garment is resewn at the markings to reveal a new and improved fit to the garment.