To add a bit more context:
The Latin alphabet is pretty well-suited for Latin, all things considered. It was adapted in antiquity to fit the phonology of the language, with new letters like G and Y invented or borrowed to better represent the sounds of Latin.
But, it's not quite perfect. There are a few contrasts in Latin that the Classical alphabet just didn't have a way to represent (at least not consistently). For example, the same letters were used for long vowels and short vowels: ALIVM with a short A means "another", but ALIVM with a long A means "garlic". Similarly, the same letters were used for vowels and semivowels: VOLVIT means "she wanted" if the second V is a vowel (approximately "woh-loo-it"), and "it rotates" if it's a semivowel (approximately "wohl-wit").
As a result, we tend to modify the alphabet in modern usage (and not just by introducing lowercase letters). For example, we can write alium versus ālium, and voluit versus volvit, and the ambiguity disappears. The Classical alphabet didn't have any distinction between I and J, or U and V, but nowadays it's common to use I and U for the vowels and J and V for the semivowels.
This is why I prefer the spelling ejus. The J represents a semivowel in this word, not a vowel. But, the spelling eius is closer to what the ancient Romans would have used, and some editors prefer it for that reason. Either way, it's representing the same Latin word, meaning "his/her/its". It doesn't change the meaning any more than switching from all-capitals to lowercase.