Culture is, most basically, the way of life of a group of people. More formally, it is shared and learned patterns of behavior. Race , conversely, refers to genetically transmitted features such as skin color, hair color, etc. One is born with race but one learns culture.
Culture change can occur internally or externally.
Internally, culture change occurs through the process of innovation. Diffusion refers to the process by which an idea or object spreads from a place of origin to other places without the necessity of migration. Think of mass communications, for example. Acculturation refers to the process of migration in which two groups of people come into contact with each other. As a result of this contact, each group is affected by some degree of merging or adapting of features.