This expression comes from 'tacking' a boat to help it to change direction. To 'change tack' or have a 'change of tack' means to change or reverse a decision, opinion or alter the course of action. "The funders had a change of tack when they saw the reality of how people were living." "We need a change of tack to encourage young people to invest in pensions." This is a common phrase you will hear n social and professional situations. Similar meaning expressions include 'a change of tactics', 'a fresh approach' and 'a change of direction'.