Error on running "adb shell wm density 240" for changing Android device density

Question

I want to resize the screen on Android device. When I run the following commands:

adb shell wm density 240

or

adb shell wm size 800x480

I get error:

/system/bin/sh: wm: not found.

Why? How can I resolve that?

I should mention that my device is rooted and its model is Asus transformer TF101

Answer 1

I changed it to:

adb shell am display-size 800x480

and it worked

Answer 2

wm (Window Manager) is not available on Jelly Bean and older devices. for pre jelly bean use

adb shell am display-density 240

or

adb shell am display-size 800x480