I replaced my hard drive myself with a 2TB one over 6 months ago, might be longer though.
Was a simple matter of buying a new one, removing old one from the box, replacing with the 2TB and started it up.
Box formatted the drive itself and started no problem at all once it had done installing what needed to be done.
Have had no problems at all since doing this. Amazing the amount that can be recorded on it compared to the 1tb that was on it originally, so let the machine do it itself.
Was going to use one from my old Sky box but bought a new one instead…