Do you mean reorganise the letter array into the most frequent? I've re done it to that now of:
char[] aLetter ={ 'e', 't', 'a', 'i', 'o', 'n', 's', 'r', 'h', 'u', 'l', 'c', 'd', 'f', 'm', 'y', 'g', 'p', 'w', 'b', 'v', 'x', 'q', 'k', 'j', 'z' };
In essence, the way you've done it is "Hardcoded" and they should be sorted by means of like LINQ and not just a pre-defined array (This will make you pass your assignment, however, is not really a good way to program)
Your array should contain something like:
A = 8.2, B = 2.3 etc.. And then sorted that way.
Doing the method you've done, have you tried to match the the two values together? For example:
Alphabet: E T A I O N S R H U I C D F M Y G P W B V X Q K J Z
Ciphertext: C Y X S M P E T U V Q L I H K W J A D O R Z B G N
?