Photoshop: how I can increase the height of a part of my image?

Firstly, increase the size of your canvas by 90 pixels probably aligning to the top would be a good idea:

Now select and move the bottom line to new bottom of the canvas. Now, this is where you have a slight problem. Both the bottom line in your image and the area which you wish to increase have a subtle angular texture (for want of a better description). I've exaggerated it here:

If you really want to have that in your final image, I'd be tempted to redraw the whole image, if you don't have access to the original. Draw the triangles with different greys, add a noise layer and a slight gradient, place that in a group, change the opacity and you're pretty much there.