How does AAVE voting work - Who approves changes and how?

People holding AAVE or stkAAVE can vote on AIPs. You can vote here, and see examples of previous AIPs;

Voting is as easy as connecting your wallet to the Aave interface, and if you have AAVE or stkAAVE, clicking on an AIP available for voting and choosing how you vote.

There are community contributors who check the code prior to voting commencing. Once an AIP is submitted and up for a vote, if it passes, no one is needed to approve or implement the change. It happens trustlessly on chain;