When you are at ground level taking pictures of tall buildings you have to point the camera upwards. Result: the buildings appear to be falling over backwards. Sometimes this can look good, sometimes it does not. In the computer you can correct it.
Select the whole image. Click on Image > Transform > Perspective. Now drag the corner anchors until you have the picture the correct shape (probably by pulling the top corners out or the bottom corners in. Double click to fix it. You will then need to crop away any waste space you have created.
If the correction you need to make is not symmetrical you will need to use Image > Transform > Skew and drag the left and right corners independently.