HELP !!! How do I replace a subject with another subject on a detailed background?

[Tony5E91]

Ok so, I'm sure anyone familiar with Deadpool sees what I'm trying to do here. Don't mind the additional layers. I'm simply trying to figure out the best, most efficient way to finish this background and complete this photo. Any suggestions? Because this has been a complete headache lol Thank you in advance.

[Myra Ferguson]

In general, to place a different subject into a photo, you would do the following:

1. You'll need the background and the subject to be on separate layers. It isn't clear from the screenshot, so if your subject and background are merged into 1 layer, duplicate that layer.
2. Select one of the selection tools such as the Object Selection tool
3. In the Options bar, select Select Subject
4. Click the Select and Mask... button to enter the Select and Mask workspace to clean up the selection
5. At the bottom of the Select and Mask workspace, set Output to Layer Mask
6.  Ctrl (Windows) / Command (macOS) + click the layer mask to make a selection from it
7. Use the Lasso tool to add to the selection that needs to be filled in on the background
8. Expand the selection by going to Select > Modify > Expand and set a pixel amount to give you some extra coverage for filling in the background
9. Go to Select > Modify > Feather and set it to the same amount to help blend the edges that you'll be filling in for the background
10. Select the background image layer
11. Go to Edit > Content-Aware Fill and use the options to help fill in the area and click OK
12. Hide the visibility of the subject layer and use other tools such as the Clone Stamp or the Healing Brush to touch up any areas that need fixing in the background
13. Turn the visibility back on for the subject layer

[Jumpenjax]

Myra Ferguson gave a very detail way to accomplish what you need. It is explained very well. Give it a go.