Information is scattered all around - here is one link -
My own experience - I use a Yihua 995D hot air station - and very sharp tweezers - very sparing amount of NC-559-Flux -
There are many You Tube videos on replacing BGA 153 emmc chips - I would not recommend re-balling unless you really want to get deep into a project…
In a nut shell - to remove - have tweezers handy - use a small nozzle on the hot air gun at 1/4" distance perpendicular or so from the chip - very minimal air volume - don’t blow the chip off the template - - moving back and forth slowly - 1 minute @ 170C, then 1 minute @ 270C then 1 minute at 360C and the chip should come off with tweezers.
I use a coin collectors microscope - $75 or so on amazon to look at the pcb and chip.
Wick and clean carefully - 99% isopropyl to clean - then after cleaning very carefully - apply a very very sparing amount of flux on the pc board - very sparing amount - then place the new chip - already balled - exactly over the template for the removed chip - again exactly over the template… Flat surface - don’t shake or bump… very low air volume / speed / heat 1minute @ 170C, then 1minute @ 270C then 1minute at 360C - the new chip might migrate slightly to adhere to the pads - let cool and go and you should be ok. Your mileage may vary - de nu5d.