The portion “…be removed…” in this question is not clear, and the distinction is important.
There is a difference between operational removal (i.e. firing anyone as an employee) and ownership removal (i.e. buying out an owner’s shares of the business).
Typically, the answer to this question will be found in the LLC’s Operating Agreement. Properly constructed, the Operating Agreement document details all of the responsibilities of the operations and ownership for an LLC.