The BlueStacks 2 allows its users, to change the size of the screen. You just have to drag the corners of windows to resize BlueStacks 2. If you have any problem while doing this, you can also use the PREFERENCES TAB to change the screen size of BlueStacks.
This feature is only available in BlueStacks 2 which is the latest version. If you are having any older version learn HOW TO UNINSTALL BLUESTACKS with backup or without backup.
Then in the next STEP, download BlueStacks 2 and install it on your device. If you are not able to understand and implement the steps written above, watch the video below.
Video From Official Source Explaining Steps to Resize BlueStacks 2