When opening GDTS for the first time, and if no Default Texture Pack exists, it will ask to get all files (excluding .dat) from the Geometry Dash Resources Folder. So if you already have a texture ...

up arrow - Moves selected image 1 pixel up. down arrow - Moves selected image 1 pixel down. left arrow - Moves selected image 1 pixel left. right arrow - Moves selected image 1 pixel right. enter - ...