The most basic way to resize the width or height of an area selected using the Crop or Free Transform Tool is to click on any of the ‘handles’ shown in ‘blue’ below.
To adjust the area’s width, click on either the ‘handles’ and, with your mouse button still held down, simply drag the handle left or right. To adjust the height, click on either the top or bottom handle and, again with your mouse button still held down, drag it up or down. However, as you will see, the image will only resize in the direction you are dragging.
To get the right/left or top/bottom sides to resize equally is simple, just click on one of the ‘blue’ handles, hold down the Alt (win) / Option (Mac) key and drag and they will resize equally in the direction you are dragging.
For total flexibility in changing the area to be cropped, use one of the corner handles (in red), hold down the Alt (win) / Option (Mac) key and drag in any direction – they will resize equally in whichever direction you are dragging. You can then make any fine adjustments to the selected are by moving it using your mouse (make sure its’ pointer is within the selected area).