However, I have recently updated to Python 3.7, and there are some changes between these versions. NPP still gives me suggestions as though I’m using Python 2.7, even though I don’t even have it installed on my computer anymore.

This is best seen when getting user input. In Python 2.7, input() was a function that would only accept and return integers as input, and raw_input() was a function that would accept any input because it would be returned as a string.
In Python 3.7, there is no such function as raw_input(). It was removed, and now input() uses strings instead of integers.
However, NPP still tells me that input() returns an integer (in a round-a-bout sort of way) and that a function called raw_input() exists and returns a string.

How do I make NPP give suggestions for Python 3 instead of Python 2?