Is there a way to change encryption scheme from AES to FHE without data leakage? So let's say that we have encrypted some data using symmetric encryption in this case AES. And we want to change it to homomorphic encryption but without decrypting the data and encrypting it again using FHE. Do you know if this is possible in any way?
If you are talking about FHE (as stated in the title, but not in the question body) then yes, this is possible.
Encrypt the symmetric key $k$ that was used to originally encrypt the data as well as the symmetric ciphertext $c$ under the FHE public key. Then homomorphically evaluate the decryption circuit of the symmetric encryption scheme on those ciphertexts. By the correctness of the FHE scheme the result will be a ciphertext encrypting the original data under the FHE public key.