What would you change in Heroes of Might and Magic IV?

Yeah, then higher-level creatures won't be needed at all.

How many times do you need to upgrade the small one so that the big one becomes completely unnecessary?

They also changed the classes of heroes, so they know how to do it.

Changing and adding are different things. They also know how to change magic, but they can't add new spells.

And what is considered the latest version? I was talking about 3.51 - they seem to disappear there.

Currently, version 3.55 is in open beta testing.