I was wondering if there was a reason you change the covers

[Vertical Inc]

I was wondering if there was a reason you change the covers of some of your series. I see this happen with a lot of other manga companies as well. Sometimes it's for the better, and sometimes for worse. I'm just curious as to why they're changed.

The reasons vary from company to company, book to book.
But here are some reasons why we do that:
There are no files for the Japanese cover (Gundam the Origin, Paradise Kiss)
The Japanese cover has nudity or depicts graphic violence (Helter Skelter, In Clothes Called Fat)
The Japanese cover is not visually relevant to the content (7 Billion Needles)
Request by Author (Peepo Choo vol 1)
The Japanese covers are not very creative (Tezuka releases)
To be completely honest, in a perfect world I would change almost every cover. Markets are different. Perspecitves on style and design are different in every region as well. The traditional world of publishing almost always sees covers change between paperbacks and hardcovers. But for some reason manga is different (even though the Japanese change cover designs for different editions all the time. Looks at his Sailor Moon, Urusei Yatsura, Maison Ikkoku and Akira re-releases).