How had the British government ruling the colonies changed for the worse by 1776?
Objectively speaking, it is hard to say for certain that the government had turned for the worse. From the colonies' point of view, however, it most certainly had. Mostly, it had done this by A) taxing the colonies more and B) enforcing laws more strictly.
In the times before the French and Indian War, the government had practiced what historians call "benign neglect," pretty much leaving the colonies alone. This got the colonists used to ruling themselves and having British laws lightly enforced. After the French and Indian War, this changed.
After the war, the British government decided that it needed more revenue from the colonies. To do that, it had to tax them and to enforce trade laws, in particular, more forcefully. It imposed various taxes like the Stamp Tax and it did things like setting up vice-admiralty courts to try people suspected of smuggling. These courts were less solicitous of the rights of the accused and did not have jury trials. This made them more likely to convict in any particular trial.
Because the British government taxed the colonists more and enforced other laws more strictly, it seemed to the colonists to have changed for the worse.