I have a Fuji Nevada 4.0 frame that I didn't wanna part with so I've spent the last several weeks upgrading all of the original parts. I'm wondering how difficult it is to switch out what I'm assuming is a square taper bottom bracket in order to upgrade to a better chainring, crankset, etc. I've tried reading a ton of material online about bottom brackets but it seems like the most complicated part of the bike that I'm having trouble grasping and I'm a little too afraid to simply take the whole thing apart to figure out what I have. Do I have to stay with a square taper bottom bracket or can I simply buy any new type of model? Any information would be greatly appreciated!

P.S. I was thinking about buying an entirely new bike, but I love to take things apart and rebuild it in order to have a better understanding of it. It helps me to appreciate the sport a whole lot more.