SilverStripe 2.4.7

Hi

I got a request from my client to enlarge the thumbnails in the assets section. After looking through the code I found this which I assumed was the right line to change.

/**
	 * The width of an image thumbnail in a strip.
	 * @var int
	 */
	public static $strip_thumbnail_width = 50;
	
	/**
	 * The height of an image thumbnail in a strip.
	 * @var int
	 */
	public static $strip_thumbnail_height = 50;
	
	/**
	 * The width of an image thumbnail in the CMS.
	 * @var int
	 */
	public static $cms_thumbnail_width = 100;
	
	/**
	 * The height of an image thumbnail in the CMS.
	 */
	public static $cms_thumbnail_height = 100;
	
	/**
	 * The width of an image thumbnail in the Asset section.
	 */
	public static $asset_thumbnail_width = 100;
	
	/**
	 * The height of an image thumbnail in the Asset section.
	 */
	public static $asset_thumbnail_height = 100;
	
	/**
	 * The width of an image preview in the Asset section.
	 */
	public static $asset_preview_width = 400;
	
	/**
	 * The height of an image preview in the Asset section.
	 */
	public static $asset_preview_height = 200;

But no matter which value I changed it seemed to have no effect. Can anyone shed some light on this? Can I misunderstanding something fundamental?

The other request I got was to only allow the admin to upload or delete files from the assets section. Again I looked through the code and found if blocks which specified things like

<% if Can(delete) %>

My questions is where do I set these permissions to say that only the admin can delete, edit, etc?

Thanks