Britain changed its colonial policies for several reasons in 1763. The first, and perhaps most obvious, is that the Seven Years' War, called the French and Indian War in the colonies, ended with a British victory that dramatically increased the size of their American holdings. The Treaty of Paris that ended the war gave the British control of the trans-Appalachian West all the way to the Mississippi, as well as French holdings in Canada. Great Britain thus did not have to worry about an enemy on the American continent, and a key feature of their policy was to remove the formerly large military presence from the frontier. In order to mitigate the possibility of military conflict with Native Americans, the Crown issued the Proclamation of 1763, which banned settlement west of the Appalachian Mountains. This proved a provocative measure, as it ran afoul of the desire of colonists to settle in the Ohio Valley in particular.

This was part of a broader effort to tighten British control over the colonies in the wake of the war. The war had been very expensive and led to a desire in Parliament and among the King's ministers to regulate the lucrative trade with the colonies in addition to reducing expenditures on them. The Sugar Act sought to rationalize the sugar trade by cracking down on smuggling (but actually lowering the tax on imported sugar.) One year later, in 1765, the Stamp Act aroused considerable controversy in the colonies by levying a direct tax on the colonists. This was a clear attempt to raise more revenue from the colonies, but one which colonial writers argued was contrary to their rights as British subjects.

Britain had to change its colonial policies after the Seven Years War ended in 1763.  The country had been fighting off and on for over a hundred years with Spain and France.  The American colonists, while providing military assistance, were dodging taxes and navigation acts whenever possible in order to help their own profits.  British officials got to see what the policy of salutary neglect meant firsthand when they were in America during the war, and they did not report back favorably to Parliament.  These officials claimed that the British subjects in America were not paying their fair share.  They also claimed that these same colonists were the primary beneficiaries of British protection from enemy nations and Indian tribes.  Parliament agreed and began to clamp down severely on American autonomy by insisting on tax collection and keeping the colonists close to the coast in order to make revenue collection easier.  The colonists, who were used to the old policy of salutary neglect, resisted because they thought the tax dollars would be better used at home.  This would ultimately lead to the American Revolution.  

Great Britain changed some of its colonial policies after 1763 for several reasons. One reason why the British established their colonies was to make money. However, the colonies were becoming more expensive to run. After the French and Indian War ended, there was a growing concern that the Native Americans would attack the colonies. Most Native Americans were friendlier with the French. They believed the British wanted to take their land. Since the French gave the British some of their land in North America, the Native Americans were unhappy. As a result, the British needed to increase their military presence in the colonies to protect the colonists from possible attacks by the Native Americans. The British believed that since the colonists were benefiting from this protection, they should help pay for it. This led to new tax laws. The British also required the colonists to provide housing for the soldiers who were protecting them.

Another reason for changing its colonial policies is that the British realized that by not closely enforcing the Navigation Acts, they were losing money. Since it was becoming more expensive to run the colonies, the British decided to enforce these laws more closely. The colonists weren’t pleased with this change because that had been able to smuggle items into the colonies for many years.

Thus, the growing costs associated with running the colonies and the belief that the colonists were benefitting from the British presence were factors that encouraged the British to change some of its policies regarding the colonies after 1763.

Britain changed its policies because of the impact of the Seven Years' War, which was known in America as the French and Indian War.  After this war, Britain needed more help from the colonies to help defray the costs of the war and of the new demands that winning the war put on British finances.

Before the war, the British had pursued a policy of "salutary neglect" towards the colonies.  They didn't tax the colonies much and they didn't enforce laws like the Navigation Acts very strongly.

After the war, the British needed more revenue from the colonies to pay for military costs.  Therefore, they started to impose new taxes like the Stamp Tax.  They also started to enforce laws more strictly so that Americans could not evade things like the Navigation Acts that helped Britain.

The change in British policy in 1763, then, was caused by the financial needs of the British government that arose from the Seven Years' War.