He must not replace it or exchange it, either good for bad or bad for good. But if he does substitute one animal for another, both that animal and its substitute will be holy.
Jewish Publication Society of America Version (JPS1917) - Leviticus 27:10 >He shall not alter it, nor change it, a good for a bad, or a bad for a good; and if he shall at all change beast for beast, then both it and that for which it is changed shall be holy.