Mark a line on how short you want it to be. (This one was longer than my waist and I wanted exactly where my waist was).
Flip it over and cut the BACK part (and only the back part) all of the way up to the line you made before.
Cut cut cut 😗✂
Mark the middle of the shirt by folding it and placing something in the middle.
Cut along the middle marked by the item from the previous step.
Now cut two triangles from the two flaps.
Flip it over and tie it!
I cut just a little away some of the seam (I don't want it too low since I'm wearing this for school).
... And the same for the sleeves!
Here's a before and after.