Updated: May 2, 2021
For this demonstration, I used a cardigan that I found at Family Thrift Center!
Step 1: Try the top on to see the fit of it and make a mark at where you want to crop it.
(keep in mind that you will also have to hem or surge the material, so leave about an inch on)
Step 2: Use a measuring tape to mark the crop across the entire cardigan with straight pins
Step 3: Use a serger to cut off the material or hem it to prevent fraying