First of all, upgrading to a m.2 pcie ssd is not going to make any difference in game loading times:
View: https://www.youtube.com/watch?v=4DKLA7w9eeA
But, if you want to, the best would be a 1tb samsung m.2 980 PRO pcie4 device:
https://www.newegg.com/samsung-1tb-980-pro/p/N82E16820147790?quicklink=true
Samsung seems to be the most reliable ssd out there.
To convert, use the samsung ssd migration app to move your C drive.
Here is a link to the app and instructions:
Download various software related to your product, including Samsung Magician, designed for use with Samsung's memory products, and find related information.
www.samsung.com
Look for youtube instructions on the mechanics.
Here is one(which I have not watched)
View: https://www.youtube.com/watch?v=eKeUk6jqE6I