To retrofit a machine or a building means to put new parts or new equipment in it after it has been in use for some time, especially to improve its safety or make it work better.
例句
Much of this business involves retrofitting existing planes...这项业务主要是改造更新现有的飞机。Damaged houses have been repaired, roads repaved and buildings retrofitted.受损的房子已经修好，公路重铺了，大楼也翻新了。