You can configure the maximum allowed size for a BLOB by setting the "MaxBinaryTransferSize" parameter in the $AUTOUSER/config.$AUTOSERV file.
The value for the "MaxBinaryTransferSize" parameter is in MB and the default is 1024.
The parameter is not present in the config file by default. If it is not already present, you can add it.
It is used by the Application Server only, so it should be set on all Application Server machines present in the AE instance.
Restart the Application Server for the change to take effect.