How exactly do I change the parameters of a style
'to use a 0.75-point expanded character spacing and center alignment' ?

I know that in Home > Styles, a click on the arrow gives a window
with all the styles in the current document. At the bottom there are
three icons, the rightmost of which is 'Manage Styles'.
A click on that, and its tab 'Set Defaults', does indeed show 'Alignment'
with 'Centered' in the drop-down menu.
But where do I specify a "0.75-point expanded character spacing" ?

Thanks.