Used my picture, cut out the background to add the source image
step 2 of 4
Matched the colour and brightness of the two images. Cut various parts from the source image to change the roofs of the buildings to match. Replaced the rocks on the sea
step 3 of 4
Cut parts of the sky to make the sea bluer. Then and added photo filter blue to match the colours, merged down and cloned in areas .Adjusted the brightness and contrasts
step 4 of 4
made a new duplicate layer added a high pass filter and changed the blend mode to colour burn, turning down the opacity to suit