Hi im working on an single cover for an artist. They gave me an image with bad quality, that i needed to change so i did and put layer on it. But my question is can you make all the layers or just the image in Very good quality? How do i do it in photoshop?
You can't make a good-quality image if your source is a bad-quality image. Your artist needs to give you better source material. If they have nothing else to give you, the best you can do is to see if you can add some effects to make the poor quality look intentional.
You can't make a silk purse out of a sow's ear. Obtain some high quality, royalty free images from Adobe Stock or other image houses and then composite them to create your own custom artwork. See this Photoshop Training Channel tutorial on YouTube.