I want to learn to do alterations. How?

By “reduce,” do you mean you want to let it out?

Removing shoulder pads is simple. If they’re sewn inside the garmet, find the inner seam that connects the lining to the jacket itself, remove only the number of stitches necessary, take the pad out and whip stitch (or choose a stitch, I suppose) and sew the area back together. They may also be sewn through, so you may have to remove some of those stitches too.

The easiest way to fix something to big in the shoulders, assuming it has a seam down the middle of the back, is to take that in. You could also undo the seam connecting the shoulder fabric to the sleeve and cut some of that down, or sew it into itself, then reattach the sleeve.

Where are the seams in this jacket, what is it made of, and what exactly do you want to do? A little more description and I should be able to give some better advice.

Maybe you could apprentice at a local tailor’s shop for a while, just to learn the trade for yourself. If you get really good at it, you could make a nice side income for yourself by altering friend’s clothing. I wish I knew someone who could do this for me : )

Try a sewing class at your local community college.

I think to learn how to ‘alter’ clothing that is already made is an ‘art’ that isn’t necessarily taught in a class and if you haven’t learned from another person that knows how to do it then You either have to take a chance and try it yourself or leave it alone and give to someone that the garment will fit.

I took lots of clothing and sewing classes while growing up and learned even tailoring items but it did not use items that were pre-made! They were all classes on how to make them from scratch.

In this day an age, it seems like it is almost the same cost or more to sew items depending on what you are making vs going an buying it from a store. Fabrics aren’t that inexpensive especially the ‘nicer’ ones.