If 75% of the users want something, of course they can do that. They uninstall Bitcoin, implement a new software with the new rules, and install it. This become

If 75% of the users want something, of course they can do that. They uninstall Bitcoin, implement a new software with the new rules, and install it. This becomes the new "Bitcoin". That is called a hard fork. You can't prevent that because it literally means people just chose to use something else. They may even keep the name and call the new thing Bitcoin, for what it is worth.