Not sure about what you mean by the difference between scaling and enlarging...
If you want to change the global size (all dimensions scaled the same way) use ANALYSIS/UnitsDimensions. Here you can set a metric value.
You can do the same on a object by EDIT/Transform while keeping other objects in the scene untouched. Here you can do a proportional scaling and non-poportional scaling (check UniformScaling in the tool's properties). There you can also set numerical values (clicking on the displayed numbers) ScaleX, ScaleY, ScaleZ is a factor the current size is multiplied. SixeX, SizeY, SizeZ ist the target length of the bounding box (World- or LocalBB depends on the setting in the widget).
Or do you mean extrusion to add a length while the rest of the object is not deformed? In this case (e.g to make a pedestal of a sculpture higher) you can use SELECT: Select the region to extrude and run SELECT/Deform/Transform) Here you can't put in a numeric value. But the Transform widget has a snapping function you can en/disable by clicking on the little S circle. You can set the snapping increments using the Up and Down keys on your keyboard while click and hold a transformation arrow. The A circle toggles absolute and relative distances.