Basically it works like this.
- Install Impulse and launch it.
- Log in with the same account you're using for the forums (so, your e-mail and password).
- Click the Impulse orb in the top left corner of Impulse, and select "Register a product.."
- Put in your Sins serial # (and select Sins from the dropdown list if it still asks you to do that).
- When that's done, Sins will show up in the "My Games" tab.
- It should also have a yellow (!) icon over it to indicate that an update is available.
- Click the icon, and then in the lower right there will be an "Update" button. Clicky to patch the game.
- When no update is available, you won't have the (!) icon and that button in the lower right will launch the game.
I think I got everything.
Hope it helps!