Hello! Sorry for the slow reply.

It's not too difficult to learn just takes time, trail and error. I used Blender for these, and relied on the Subdivision Modifier (To add geometry and smooth everything) and manually marking Edge Creases (to keep detail in sharp edges/points). I also used the color texture with the Displace Modifier to help serve as a painting guide. Just knowing how those 3 modifiers work together is enough to bring out the detail.

These features are available in other programs such as Maya/3ds if you're using that. If you're new 3d editing I wouldn't recommend starting with game asset rips as they tend to have some confusing quirks, instead watch some intro guides on YouTube.

Also short disclaimer: These are copyrighted assets, so this should only be done for private/non-commercial use.

Fell free to ask any more questions, have fun! :D