How to modify the absolute value of a dimension?

1. Set a dimension annotation on the feature whose size you want to change:

2. Click on PULL/MOVE tool and select one of the faces/edges you want to use as reference to modify the geometry

3. You will notice a 'bubble' appear next to the annotation, click on it and enter a new value for that dimension.

The difference will be shown and the absolute value will be in effect when you click keyboard enter.