Figure 1 shows the original image shot with a wide-angle lens or the zoom lens has been "zoomed-out."  The convergent lines of the vertical structures are a common perspective distortion when you zoom-out and shoot a building because there are vanishing points where parallel lines will converge.  In fact, the mathematics of the situation requires that distortion must appear.  If the shot had been taken by "zooming-in" with a more powerful lens, this type of distortion would not be apparent.  However, you rarely can get far enough away to take the photo with a powerful zoom, and wide-angle depth affects are often interesting.  Fig. 2 shows a corrected image done in Photoshop Elements.
 
 

Fig.1 Original image with perspective distortion.

Fig. 2 Correction of perspective distortion.

Correcting perspective distortion.
Before doing a distortion correction, I recommend do most all of the color corrections, but not the sharpening using the UnSharp Mask.  Duplicate or SaveAs the image file to a new file.  If you screw up the correction, the screw up can be a disaster that can not be corrected.  After the correction, then you can Sharpen the image.

• View > Grid.  This will display a rectangular grid over the image, which will help us align the corrected image.
• Get some working space.  Click on the Zoom tool.  This is the magnifying glass icon at the bottom of the tools.
• Click on the button "Fit on Screen."
• Click on the little magnifying glass the has a dash or negative sign in it (up near the top in the tool properties section.)
• click on the image.  You should now have some gray space between the image boundary and the window that contains it.  If only a small sliver of gray space is showing, click on the image again.  This is shown in Fig. 3.
• Image > Transform > Free Transform.  You may get a message about Layers, so just say OK.
• Holding down the Ctrl-Key, drag the control points (on the corners and mid-points of the edges) to change the shape. For this example, I moved the upper-left corner to the left and down, and then moved the upper-right control point upward and to the right, as shown in Fig. 4.
• Before accepting the transformation, carefully check the entire image for any unwanted distortions.  Even though the vertical lines of the phone booth and Big Ben are aligned vertically, it is possible that the clock is no longer a circle.  It is very common for a circular shape to be deformed into an elliptic shape.
• You will be asked if you want to accept the transformation.  Say OK if you like what you did.
• You may want to crop the final image.

Fig. 3 Gray space shown, together with the control points.

Fig. 4 Deformation after moving the upper-left and the upper-right control points.