Hi Mark, you can use Transfom / Scale / Scale 1D to stretch a model to be scaled in one direction only.

But be aware that if you have something like a circular hole, it will also get stretched in that same direction and become an elliptical hole.

If you want to lengthen something without causing any deformation to existing pieces, then usually for that you will just build an extension and use Boolean Union to attach the extension to the main piece.

So for example on your piece here if you want this to be taller:



You can select that face, and run Extrude on it to punch it out into a new solid like this:



Now Union those pieces together.

Does that do what you need?

- Michael