Debranding and Rooting are 2 different things.
For the ability to upgrade to 2.3.3, you first want to Root your phone.
You can do this on Android 2.1 using the SuperOneClick application. This will allow you obtain root level access on your device.
From there you will be able to install any version of 2.3.3 out there.
Once you get the generic 2.3.3 gb version of the phone, it won't have any company "branding" on it such as their start up logo or operator bloatware.