Java using AES 256 and 128 Symmetric-key encryption

I am new in cipher technology. I found this code to do Symmetric Encryption.

byte[] key = //... secret sequence of bytes
byte[] dataToSend = ...
Cipher c = Cipher.getInstance("AES");
SecretKeySpec k = new SecretKeySpec(key, "AES");
c.init(Cipher.ENCRYPT_MODE, k);
byte[] encryptedData = c.doFinal(dataToSend);

Its working. Here I can use my own password. And thats what exactly I needed. But I dont know how to do 128 or 256 Symmetric Enctryption. How can I use 128 and 256 key into my code ?