Step 1: Select the Quick Selection Tool.
2. Switch to the Quick Selection Tool. (Pic 1)
3. Select the face using this tool.(Pic 2)
Step 2: Copy and Pasting
1. Copy and Paste the face onto the other image. (Pic 1)
2. Drag the face into the right position and use free transform to fit it. (Pic 2)
Step 3: Erase!
1. Grab the erase tool, use 0% hardness. (Pic 1)
2. Erase the parts that aren't needed. (Pic 2)
Step 4: Levels P1
1. Go to Layer>New Adjustment Layer>Levels (Pic 1)
2. Make sure you check "Use previous layer to Create Clipping Mask" (Pic 2)
Step 5: Levels P2
1. Using the levels, make the skin tone as similar as possible. Sometimes more editing is required. (Pic 1 + 2)
Step 6: Done!
Now you're done, and sorta creeped out...