What have you tried? Hard to make suggestions without some code.
app.activeDocument.rulerUnits = RulerUnits.Points;
Did you look at the first item in the similar list in the sidebar. You can only set the ruler units (listed in the object model as read only) on the creation of a document with a document preset. You would have to make a new document with the desired properties and copy the page items to that new document. There is a script called MoveItem.jsx installed with AICS3&4 which demonstrates this.