Hello Said,
Your encrypted files are encrypted in free subscription that means AES-128 bit Algorithm.
Now, Just open the Encrypted file(s) and update the content of the file(s) then save and close the file(s). Now your encrypted files) upgrade to AES-256 bit Algorithm(Premium subscription).
Or
You can also upgrade the encrypted files from AES-128 to AES-256 by using the feature called ”Upgrade 1.x and AES-128 files”. You can see that option under the file menu. After choosing that option, you will be prompted to select the files. After selecting the files, AxCrypt will upgrade the encryption level from AES-128 to AES-256
If the above doesn’t help, please write an email to our support team support@axcrypt.net.