Hi, I hope here is what you need:
Settings -> Table Appearance -> Table Display -> Checkbox 'Show Stack Values in Big Blinds for Cash Games'
Settings -> Table Appearance -> Table Display -> Checkbox 'Show Stack Values in Big Blinds for Tourneys'
Just to add that once you have set the option for showing your stack in blinds you can click on your balance and freely switch between chips and blinds which I find useful.