Many texture modifications don't provide a .ytd texture archive but only a specific texture, usually in a format like .dds or .png. To replace original textures with those modified ones, open the .ytd file you want edit it in OpenIV's texture editor. To open it, either double click the .ytd file or use right click and select "edit". In the texture editor, click on a texture to select it. Then, click the replace button and select the texture you want to replace it with. You can then change compression or mipmaps. These options are explained in seperate guides (Texture Compression and Mipmaps). After the texture has been replaced, the modified .ytd file has to be saved.