How to upgrade custom plugin from ckeditor 2.x to 3.x?

In ckeditor 2.x, we are using the following js code to register custom plugin.

FCKCommands.RegisterCommand('MediaLibrary',new FCKDialogCommand( 'MediaLibrary', FCKLang["MediaLibraryBtn"], '../../Pages/MediaLibrary/MediaSelection.aspx', 850, 600 ) ) ;
var oMediaLibrary=new FCKToolbarButton('MediaLibrary',null,FCKLang["MediaLibraryBtn"],null,false,true,74);
oMediaLibrary.IconPath = FCKConfig.PluginsPath + 'medialibrary/fck_medialibrary.gif' ;
FCKToolbarItems.RegisterItem('MediaLibrary',oMediaLibrary);

var FCKMediaLibrary = new Object() ;
FCKMediaLibrary.Add = function( mediaText )
{
var coText = FCK.CreateElement('SPAN');
coText.className = 'media-library-container';
coText.innerHTML = mediaText;

}

but how can we upgrade this plugin to ckeditor 3.x??
We cannot find any example for upgrade, please help us.
Thanks a lot.