trade up/down
phrasal verb with trade verb uk/treɪd/ us/treɪd/
买更贵／更便宜的东西（通常指房子或汽车）
to buy something, usually a house or car, that is of higher or lower value than the one you already have
Financial advisers warn against trading up to a larger home unless you are sure you can afford it. 财务顾问们警告说除非确信付得起，不要换更大的房子。