I've downloaded a plugin to change the Image manger (http://www.saulmade.nl/FCKeditor/FCKPlugins.php) and it's exactly what I was looking for. There is however one problem I'm having with it...
Once I've inserted an image I right click on it and go Image Properties and it opens with the default FCKeditor file manager. How could I make this open with the Image Manager plugin?
Change Right Click Menu