> What do you call those alteration?
Better:
- What do you call these alterations?
In speech, without gestures, "those" tends to look backwards, but we
haven't read anything to refer back to yet.
> 1. make the garment smaller (take it in?)
> 2. Make the garment larger (let it out?)
Yes to both.
The question is better put as:
- make a garment bigger
"the" implies that we are discussing a specific, known garment.

Signature
David
Eric Walker - 19 Jul 2009 23:41 GMT
[...]
> "the" implies that we are discussing a specific, known garment.
Not so: the definite article can be, and very commonly is, used for more
or less indefinite items:
Keep your eye on the ball.
(And many other such sayings--"the proof of a pudding", &c.)
The sense of "the" in such cases is just as it is in the OP's sample
sentence: a particular but unspecified specimen of a general class.

Signature
Cordially,
Eric Walker, Owlcroft House
http://owlcroft.com/english/
>2. Make the garment larger (let it out?)
Note that something can only be "let out" by as much fabric as there is
extra in pleats, darts, or the folds of the seams. If you have to add
new material to enlarge it, that's not letting it out. I've usually
heard that called "adding a panel." I don't think there's any special
jargon that describes both of these processes at once; it's just
enlarging the garment, or making it bigger.
¬R / Darla: Leftovers aren't the mark of a man. \ www.bestweb.net/~notr
Andrew Reid: Actually, they are, because that's how men's shirts button.