The change of Legendary Godzilla after Godzilla(2014) in Godzilla KOTM

'19 seems to have a slightly thinner snout and a longer neck, and of course his dorsal plates are different. He's a bit beefier too.

2019 Godzilla is more badass

2019 is bigger, more menacing (physical appearance, as well as behavior), his teeth are larger (Definitely not the same size as was stated back in 2014, so I would love it if someone calculated it for 2019's tooth size and gave a proper answer.), he acts slightly more benevolent, and he has scars before he fought Ghidorah (presumably from MUTO Prime [wish it was actually stated in the film]).

There could be more, though. I will have to look back and update it later.

2019 is bigger, his dorsal plates are different (MUTO Prime battle), he's faster, stronger, and intelligent, and even emotional. During the Boston fight, you can clearly see and hear Godzilla in pain, mostly through his high-pitched screeches after Ghidorah used his Gravity Beam Scattershot (Wing Attack), and when Ghidorah tried to absorb Mothra's energy from Godzilla. Side note, when Mothra was about to sacrifice herself, he seemed to look at her, knowing what she was about to do. After Mothra's death, he seemed to mourn her death, with him roaring twice, with the duration being short for each one, almost as if he was saying, "Moth-ra"