What is the change management? And What is the difference between HR Manager and HR business partner?

HR Manager is responsible for company while the HR business partner is responsible for the assigned business only.

HR manager is a fucntional line manager. He is responsible for recruitment & selection, orientation, training & development, employee relations, compensation & benefits, performance management, organizational development and talent management. On the other hand, HR partner is a strategic adviser for HR strategy, HR planning & designing and coordinate with other department.

The HR Manager will oversee department functions as well as manage employees. They are well-versed in the HR disciplines of compensation/benefits, training/development, recruitment and employee supervision. 

The HR Business Partner is (usually) more senior in the position of HR Manager, and are strategic in terms of organizational planning.

Ultimately, it depends how the job descriptions for the company are written, since you will see HR Managers doing the same job as the HR Business Partner.