wavelet transform at 2nd level

how can i separate and manipulate LL, HL, LH and HH components using wavedec2 function and after manipulation i want to recompose the C vector and take WAVE rec2.. so how can i do this the code is shown below

clear all;
close all;
clc;
I=imread('C:\Users\PRAKASH\Desktop\MAT_TEST\123.tif'); 
I=im2double(I);
I = imcrop(I,[0 0 320 468]);
I1=rgb2ycbcr(I);
fy=I1(:,:,1);
fcb=I1(:,:,2);
fcr=I1(:,:,3);
[C,S]=wavedec2(fy,2,'haar');

[SH,SV,SD]=detcoef2('all',C,S,2);
SL=wrcoef2('a',C,S,'haar',2);
SL=imresize(SL,0.25);

SH=.0;
SV=imresize(fcr,0.25); 
SD=SD.*0;

SL=reshape(SL,1,9360);
SH=reshape(SH,1,9360);
SV=reshape(SV,1,9360);
SD=reshape(SD,1,9360);

   C=cat(2,SL,SH,SV,SD);

   fy_r=idwt2(SL,SH,SV,SD,'haar');