The normal version I suppose. It's in English. Plz explain how to update without losing my save files. Also I have extracted the zip file
Ok, your save files should be in the "Android/data/Eternum" directory, make a backup of them somewhere else, just in case.
Then install the new version according to its instructions. Then copy your savefiles into the "documents/Ixalon/com.caribdis.eternum" directory ("NOT into the "game" folder"!) That should do it.