ok so it is the miners that have the major control?
No. Trying to find something to simply pin an "in charge" badge on in Bitcoin is an effort doomed to failure.
Bitcoin is, first and foremost, a zero-trust consensus system which assumes its peers are malicious and so it autonomously validates all the information it receives and imposes the hardcoded rules of the system all on its own. Miners are anonymous participants— they self-select and come and go as they wish— and are also generally assumed by the protocol to be malicious.
Unfortunately, it's not possible to validate _everything_ in a fully autonomous manner, because the possibility of double-spends— two transactions which spend the same Bitcoin, something prohibited by the rules— demands knowing an ordering for transactions in order to resolve which of multiple spends is the survivor. A consensus ordering cannot be determined in a fully trust-less and decentralized manner for fundamental reasons (e.g. even relativity teaches us that the order you perceive events depends on your position).
So, instead, we use a weak computational vote to choose an order, which has the benefit of being easily validated by computer so its useful as an automatic consensus tool. But Bitcoin is not a democracy, democracies are inherently oppressive if less so than the other systems that order people around against their will— the majority wolves voting to eat the minority sheep for supper— and the computational vote seldom aligns with actual people, it can be bought. The 'vote' is only used for determining transaction order, and the imposition of all the rules by all the other participants is believed and hoped to remove most of the incentives to abuse ordering influence— a kind of economic hack, because participating in the ordering requires expending scarce resource, and that effort is only rewarded if your work ends up in the chain that the network accepts.
So when you ask the question about changing the rules you have to ask about what kind of change you're talking about: If it is a change which involves tightening them— e.g. restricting transactions that previously would have been permitted— then you can achieve the change through ordering control, a super-majority (a simple majority is unsafe) of miners can use their ordering control to "infinitely delay" any transaction which doesn't meet the new rule. Sadly ordering control implies the power to censor, but on the plus side it does make adding new restrictions easier. The Bitcoin protocol was designed with many placeholder "meaningless but permitted" messages, which can later be restricted to add new features. If instead you ask about a change that would permit something which is currently forbidden, then _every_ remaining participating node must be updated. If the rule weakening shows up in a block it— and all subsequent blocks in that chain— will be completely ignored by nodes not updated to accept it. This is why miners printing themselves 100btc/block is simply equivalent to them no longer mining, at least in a world where many people run full nodes.
Cheers,
