How to solve a Rubik's cube 4х4 - Step 4

In the beginning of this stage you should have the solved upper cross.

In the end of this stage the upper layer should be solved.

Apply the formula of the second step for solution of 3x3 cube. Solve the up face. Find one of the corner pieces of the up face and locate it on the down face. Now, depending on how the colors were placed, carry out the procedure shown below.

Variant 1

Variant 2

Variant 3

Repeat the operation with three remained corner pieces of the up face.