Correct: both Michael and Micheal.
Both Michael and Micheal are variants of the same Hebrew name Mikha’el and as such it’s hard to label one as incorrect. In general, however, it can be said that the variant Michael is much more common, while Micheal is a rather local and lesser-known variant so you need to be careful. The spelling of names has its own rules and quirks, so what can be seen as a misspelling by one person, may seem like a unique name idea to another, so before you write to someone by the name, make sure you got it right!

Correct spelling

Correct spelling