Hoping to end decades of tension over the advancement of minority officers, the Boston Police Department plans to overhaul a promotion system that has been criticized for contributing to a lack of diversity in the department’s upper ranks.

Commissioner Edward F. Davis is expected to send an e-mail to officers and command staff Thursday announcing a $2.2 million initiative to ­replace a written promotion ­exam used statewide with a testing system that could ­include interviews and other components designed to provide a broader measure of leadership and potential.