You can choose the texture you want to apply in one of two ways – the most direct is to select one from the drop-down list in the middle of the Dirty Pictures window (right above all the texture settings). Textures you tag as a Favorite will appear first in the list, followed by everything else. Once you make a selection, the texture will be applied to the photo you’re working on.
You can also select a texture from a grid of thumbnail previews by clicking on the Pick Your Texture button at the top of the window. This button brings up your Texture Library, which you can use to visually browse all the available textures. Clicking on a texture thumbnail from this screen applies the selected texture, and brings you back to the main screen where you can tweak settings or confirm your choice.