If you mean the trash thing you sould search the theme's files and icons and change it from there ( remember to save it using the same name, as it is in the theme )
And buy the way,, There is alot of things you can change if you play on that theme trick .
if you want something to change in the interface ( as an extra )
You can go to :
There's alot of things you are able to change .
If you use redhat you can change the main menu icon as an excample .