You can't without losing data. A long needs 8 data, a char and a short 2. Therefore, you need 8 + 8 + 2*2 + 2 + 2 + 8*2 + 8*2 + 8*2 + 2 = 74 bytes. Even if you use only one byte per char (which is possible for ASCII characters) you still need 48 bytes.
You might be able to shrink those class members down via huffman encoding, that way you will lose nothing.
Your subject implies to me that you are looking to split up the serialized object into a byte array? If that is the case, I have to ask why? If I am misreading, can you clarify what you are looking to do and why please?
subject: Convert Object to byte array and array size should be 40