I took this really great photo and I didn't notice it at the time but someone's arm is sticking into the image. It's really distracting and I want to cover it up. The arm is over a concrete bench and it can easily be hidden. I think someone once told me I can "copy" something on an image and then paste it over whatever I want to cover up. I have Photoshop at work and I never use it. I would appreciate some detailed steps on how I can do this (FYI - I know very little about PS so please be specific). Thank you.