How did you go about adding the image files to the Wood library?
To edit the images they need to be in an In Model library. Then you should be able to edit them and change the aspect ratio. Of course that won't really make the wood grain the right side. It'll just make it appear stretched. In some cases that can work well enough to give the idea.
So apply the materials to either your model making sure you are applying them to faces and not to components. Open the components before applying the materials. Then switch to the In Model library in your Materials browser and edit the materials there. If you want to save the editing, open the secondary pane (little plus icon in the top right of the browser. Set the Secondary pane to The Woods library. Then click and drag the thumbnail from the top pane to the bottom pane. Unless you change the name of the material you'll be prompted to approve replacing the existing material with the new one.