change over
To change something drastically or completely; to convert something to a different form or method. A noun or pronoun can be used between "change" and "over." We have to have hors d'oeuvres out here because they're changing the room over for the reception. How much do you think it will cost to change over our heating system?
change over (from someone or something) (to someone or something)
to convert from something to something else; to convert from someone to someone else. We decided to change over from oil to gas heat. We changed over to gas from oil.