You can change the size of an object by getting to the Properties mask: click the right mouse button on one of the object lines (or anywhere in the object if in Navigation window), and select the command Properties.
In the Properties mask (see next image) change the size/scale of the object and click OK.
You will now see that the object dimension is changed, and optionally you may need to reposition it depending on those changes.
This way of changing dimensions lengthen/shorten (resizes) the object, entirely. This command can be used if the resize operation does not affect the graphic appearance of the object.
Another option you can use is the PropertyGrid: select the object with the left mouse button, then use the PropertyGrid fields in order to customize not only the size, but also the elevation, position, etc...
This article is valid for DomuS3D® 2017 and later versions