UV Unwrapping/Vertices

I know I'm probably repeating myself, but I have another issue to resolve. O.K.! I have created the UV maps for all the meshes in my model, but the Python script reports an error about the "struct" line being too long to write. I have been told to use "Seams", and write new script lines to resolve the issue, but I am having a hard time understanding the documentation. I'm sure it's just me, but it's very confusing. I realize that I can take 2 images in the UV map that are identical and merge them by overlapping them, but as I said, the documentation is exhausting. There must be an easier way to learn this method of condensing the UV map. I have tried to use the "Merge" function, but it insists there is only one image selected, and that I need at least 2. So I won't be merging anything for a while. But I do want to merge the identical images together, but I need to be able to flip 1 image I select to match the exact form of the second image. What I need to know is how do I "flip" a UV map image? When I "grab"
a Vertex, it simply morphs the face of the UV image. When I select a face on the image, then select linked faces, I can move the entire image, but I cannot flip it over to match the direction and shape of the identical reversed image. I want to grab an image, then flip it over. I know it's a dumb question, and it's probably in the documentation "somewhere!" I only need to know this one particular answer right now. I would appreciate any advice on this matter. Thanks for your help!