By now, all 4 bottom corners (and 4 bottom edges) are already in the bottom layer, so there are no more "moveup" or "knockdowns" moves anymore. From now on, all moves will either swap pieces around or twist them in their spot. The first step is to arrange the bottom corners in the correct positions:
~~~~Place the Bottom Front Corners~~~~ 

Turn the bottom layer 
Repeat this 
...until both lower 

R B+ L B 

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What the move does: 
You may have to repeat the sequence twice to fix the front bottom corners in place.
For you experts, there are variations to the prior sequence that yield powerful results. There is no need to memorize any of these, as all the other moves give you enough ammunition to solve the cube. But if you want to save a few moves, here they are:
Sequence: 
Result: 
B R B+ L B R+ B+ L+ B2 
The same 3 corners are swapped counterclockwise. 
B2 R B+ L B R+ B+ L+ 
The (bottom) right 2 corner cubes are swapped. 
B+ R B+ L B R+ B+ L+ B+ 
The (bottom) back 2 corner cubes are swapped. 
The two front (bottom corner) cubes should now be in place. The back ones may also be in place; but if they are not, swap them with the following move:
~~~~Swap the Bottom Rear Corners~~~~ 

B+ R B+ L

You only have to do the sequence once to swap the rear bottom corners in place.
All 4 bottom corner cubes are now in place. The next step is to twist each corner so that their bottom sides are the correct color. In the worstcase scenario, NO corner cube has a bottom side with the correct color. In this case, do the following move:
~~~~Finish (at least) One Corner Cube~~~~ 

R B R+ B

You only have to do this once. Now there is at least ONE corner cube is finished, with the right color on the bottom side.
Note: Ignore the diagram. As long as you keep the original top face on the top side, this sequence will guarantee that at least ONE bottomcorner cube will be finished afterwards.
Now it is time to finish another corner cube:
~~~~Finish the Bottom Front Corners~~~~ 

Rotate the entire 
Repeat the move: 
...until both front  
R B R+ B 

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What the move does: 
You may have to repeat the sequence twice to finish the front bottom corners.
The two front (bottom corner) cubes should now be finished. The back ones may also be done; but if they are not...
Rotate the entire 
Repeat the move: 
...until all four  
R B R+ B 

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What the move does: 
You may have to repeat the sequence twice to finish all four corners.
It is now time to solve the Bottom Edges.