Can Ethereum Change in the Future? Decentralization question

When Ethereum was created it was born into a proof of work system. There has obviously been a lot of buzz about layer 2 and proof of stake technology. My question is, since they can change from proof of work to proof of stake. What makes them from changing anything else? Are they able to change things about the technology without the community? Just curious because all my friends that are against decentralization think a change like this means centralization. If they can change this what stops them from changing other things? Please explain