To remove any unwanted items from an image, go to the “Enhance” panel on the left of the screen & click on the icon that looks like a plaster (or band aid), the spot healing tool. Now on the bottom menu (click “Tool options” if it’s not open) click on “content aware”. The letter “J” is a shortcut to get here. Now drag your mouse over the object to be removed. Do it in small increments, especially over areas which have a big difference in light & dark sections (eg. a cloudy sky) as covering a large portion at one time can produce a very fake looking end result.
“Proximity match” works very similar to the “content aware” tool.
Often the smaller the brush size, the better the results because the computer is taking a smaller sample to make the adjustments.