To see or wear a hat in your dream indicates that you are hiding an aspect of yourself or that you are covering up something. Alternatively, it represents your attitude or the various roles and responsibilities you have in your waking life. 

To dream that you are wearing different hats symbolise the many different roles you have in your waking life. Perhaps you feel you are stretched too thin and overburdened by daily responsibilities.

To dream that you are changing hats represent your changing opinions and thoughts.