I have a small hard bump on the top of my head it hasn't got any bigger it doesn't hurt when i touch it's very hard as if it's apart of my skull what

Many possibilties: Could be result of previous trauma, could be a benign tumor such as an osteoma. Would have a physician evaluate to ensure that it is innocuous.

Head: You are likely describing what is called an osteoma, an extra growth of bone that can be firm and raised - lack of pain is key as those that are painful or those that are rapidly growing need to be examined further.