DeFiner upgradeable contracts (SavingAccount.sol, Bank.sol, Accounts.sol) are governed by the ProxyAdmin contract. These three contracts can be upgraded to new implementation via ProxyAdmin. From now on this ProxyAdmin contract's ownership is transferred to the TimelockController contract (from OpenZeppelin). Hence, any upgrade of the contract will be done via TimelockController contract. The TimelockController contract also enforces a delayed execution of the scheduled requests.