Solution #1 (Step 4)

Step 4 -- Rotate U face edge pieces

You now have a green cross on the U face, but...these edge pieces may not be in the correct order. This step involves rotating them so that the can be lined up with their respective colors.

• If all 4 pieces are correct (the entire cube is correct except for four corner pieces on the top layer), then do nothing.
• If 1 piece is correct, then rotate the whole cube so that this piece is in the UL position (make sure green is still on the top). If the remaining 3 edge pieces need to be rotated clockwise, apply R2 D' U2 R' L F2 R L' D R2. If the pieces need to be rotated counter-clockwise, apply R2 D' R' L F2 R L' U2 D R2.
• If 2 "adjacent" edge pieces (by "adjacent" here I mean pairs such as UF and UL, or UB and UL, and not UF and UB, or UR and UL), then rotate the U face so that only 1 edge piece is correct, and follow that rule.
• If 2 opposite (i.e. not adjacent!) edge pieces are correct, then apply U or U' and follow the rule for 0 edge pieces correct.
  If 0 edge pieces are correct, turn the U face so that: for the UF piece (which can be any piece), the F side of that piece is the same color as the R face center. Now apply R2 D2 B2 D L2 F2 L2 F2 L2 F2 D' B2 D2 R2.
  

The four U face edge pieces should now be in the correct place. The cube should be all correct now except for the four corner pieces on the U face.