If someone who's already been working night shifts at this Amazon wanted to switch to day shift, how would they go about it and would their pay change?

The pay difference is 2 dollars more than your base pay, and I'm pretty sure you would talk to HR, tell them your needing to switch and or just apply the same way you did for the job you have and go through that process, since your already an employee I'm sure you wouldn't have to go through all the new hire and first day.

You would do an internal transfer, and apply for a dayshift position and you would lose your shift differential which would be $50-80 per pay cycle. It's not hard, HR can help you with the actual process.

They would either have to wait until a set of days off or have to wait the next day shift and the next night shift then start the following day shift. And yes, nightshift makes a few dollars more an hour.