Uw' (meaning turn only 2 layers instead of 3 or 1) R U R' F R' F' R Uw
If you get OLL parity, the alg is Rw U2 x (meaning rotate the entire cube up) Rw U2 Rw U2 Rw' U2 Lw U2 Rw' U2 Rw U2 Rw' U2 Rw'
If you get PLL parity, the alg is 2R2 (turn the middle slice on the right side, or whatever side is mentioned) U2 2R2 Uw2 2R2 Uw2
Solve the 4x4 Rubik's Revenge step by step: build the centers, pair the edges, finish it like a 3x3 and fix the two parity cases, with pictures for each step.