To install anything other than T-Mobile's build you'll need to root the device. But before you go off and learn about that (methods depend on the phone, sometimes on the carrier as well) that's not enough by itself. Android needs to be built for the specific device, so the first questions is has anyone built a "custom ROM" for this model based on the Android Open Source Programme (AOSP), and if they have is the ROM actually stable/does it have problems of its own? There's no point going to a lot of work if what you want isn't available. Also do you use apps that don't work on rooted devices (many banking/payment/media apps), and if you do does a workaround exist that enables the ones you use to work on the ROM you want to install?
Remember that the pre-installed apps live in a different partition to your own apps, so uninstalling them by itself does not give you more space (the system partition won't get smaller if you remove them). If they can be disabled (which is usually possible without root) then they can't use any of your space, power or RAM, which is in practice as good as uninstalling them.
I'm not trying to dissuade them from doing this, just suggesting that you do a little bit of research and find out what is possible for you both with and without root, then decide what is best for you.
