There is no possibility to merge the two AxCrypt accounts into one.
You can achieve the same by deleting one AxCrypt account. To delete your account, Please sign in at https://account.axcrypt.net/Home/Login and do so using the ‘Delete AxCrypt ID’ function under ‘Settings’. Be sure to decrypt any encrypted documents before doing so.
After deleting the account, use the another AxCrypt account to do AxCrypting.
Still you can open/decrypt the deleted AxCrypt account encrypted files with the file password.
AxCrypt will allow the users to decrypt the encrypted file with the original password which is used for encryption. If the file was encrypted with a different password than your sign in password, then you have to enter the file password while viewing/decrypting the encrypted file.
Once opened the file password asked files, Just update the contents of the files. Now those files will be encrypted with your account password. Hereinafter AxCrypt will not ask the file password for the updated files(which are all asked file password).