How to change the editor size of CKEditor?

Just go to ckeditor folder and find config.js

    CKEDITOR.editorConfig = function( config ) {
    // Define changes to default configuration here. For example:
    // config.language = 'fr';
    // config.uiColor = '#AADC6E';
     config.height = '80vh';

};

This will resize your ckeditor based on screen size.

try following

To achieve this, use the resize function to define the dimensions of the editor interface, assigning the window a width and height value in pixels or CSS-accepted units.

// Set editor width to 100% and height to 350px.
editor.resize( '100%', '350' )

While setting the height value, use the isContentHeight parameter to decide whether the value applies to the whole editor interface or just the editing area.

// The height value now applies to the editing area.
editor.resize( '100%', '350', true )

http://docs.cksource.com/CKEditor_3.x/Howto/Editor_Size_On_The_Fly