i have multisite with many blog. i can display the post

hi, i have multisite with many blog. i can display the post thumbnail, but the thumbnail size is 150px X 150px. so, how to resize my post thumbnail? and this is my code in functions.php

if( function_exists( 'add_theme_support' ) ) {

	add_theme_support( 'post-thumbnails' );
	add_theme_support( 'homepostthumbnails' ); 

  add_image_size( 'thumbone', 55, 45, true );
  add_image_size( 'thumbtwo', 418, 215, true );
  }

thank's