It's easy. Just switch the cards, connect the cables, and then turn your rig on. It will automatically install your GPU driver for you. You may need to have GeForce Experience already installed before you do this to make it easier, but I'm not sure. It is easy to navigate--I have switched out GPUs a few times and Nvidia makes it easy. As for Tweak II, you probably won't need to reinstall it, but you ought to make sure you have the latest one.
