First - are you sure it's a 4gb? You want to be sure!
When it comes to Corona consoles, there are a few questions that you need to answer to make sure that you have the right supplies in order to successfully RGH the console.
-Is my console a 4gb Nand, or 16mb Nand?
-Does my console have normal in-tact post out, or will I need a postfix adapter?
The first video below will help you answer both of those questions:
How to identify if you have a 4gb or 16mb console + if you need a postfix adapter:
Now that you're sure you have a 4gb Corona, you need a 4gb R/W tool. Options include the SD tool or 4gb tool by element18592, Maxiumus 4gb r/w kit, Xecuter 4gb r/w kit, or even a DIY reader
you should also take the time to figure out if you'll need a postfix adapter or not
Static reference images for determining if you have a 4gb nand or 16mb nand Corona, and below that how to determine if you need a postfix adapter: