That's all, Why does upsampling improve the resolution and signal-to-noise ratio? What makes it so good for noise-shaping
Upsampling is useful for noise shaping because it gives you some space in the spectrum for you to shape or steer the noise into.
Suppose your application space is audio. You need to sample at least 40 kHz (or 44.1 or 48 kHz). So suppose it was upsampled to 96 kHz, instead. In the bit-reduction operation (quantization) much or most of that quantization noise can be steered into the top octave (from 20 kHz to 48 kHz) and much less of it remains in the bottom 10 octaves (from 20 Hz to 20 kHz) which is where we are hearing stuff.