Smart contracts, as automatically executed computer transaction protocols, are widely applied in blockchain networks to implement various types of business logic. However, the strict immutability of blockchain poses significant challenges for smart contract maintenance, making upgradeability a prominent research topic. This study focuses on upgradeable smart contracts, systematically reviewing their development status both domestically and internationally, and introducing seven mainstream upgradeable contract models. The research is summarized from four key perspectives: upgradeable smart contracts, application requirements, upgrade frameworks, and security oversight. It covers multiple stages, including design, implementation, testing, deployment, and maintenance. The goal is to provide insights and references for the further development of blockchain applications.