1. Drag and drop your source Bitmap in the 2D View (and choose "Load in "Main Input" tweak) or find the "Main Input" parameter at the top of the parameters panel and browse for your texture.
2. You can easily preview multiple outputs at once by splitting the 2d View through the top right menu.
You can then render all your textures at once in any format through the Export menu.
Choose a naming pattern, select the outputs you want to save and hit "Export as Bitmap".