Merge elements from one image into another with transparency preseved

Simple task for someone who is good with photoshop. Ok the main image is '[login to view URL]'. You will see that it is a transparent masked image of a sofa, with thick arms. The second is same type of image but it has really thin padded arms on both sides. What i want is the final image to be '[login to view URL]', without the thick arms, instead it should have the slim padded arms from the second image. Please take care that the final image should also be same transparent so that it can be given any color later on by applying any layer behind the sofa image, and the thick arm shadows are removed from the image so that it looks good. I have attached a test-color-layer file, which you can put as a layer behind the sofa image, and see that the sofa acquires the background color. I will award the project containing 50 such images, to the person who can show me the image i desire from the attached files, keeping the file size to minimum as possible but having good results.