改朝换代 is a four-character set phrase (成语) meaning 'dynastic change' or 'regime change' — the replacement of one ruling dynasty or government by another. It's used both literally for historical dynastic transitions and figuratively for major leadership or system overhauls in organizations. The literal translation 'change the dynasty, exchange the generation' is misleading because it's not about changing generations of people — it's about the transfer of power between ruling houses or regimes.