Sentence:  They had lunch at a sidewalk cafe overlooking the intersection of two broad , busy , unpicturesque streets , and coming home they got lost in the Metro ; it took them over an hour to get back to the station where they should have <WSD>changed</WSD> , in order to take the line that went to the Place Redoute . 
Meaning of the word marked with <WSD> tags:  change from one vehicle or transportation line to another