It's very easy in Blesta to provide the client the information about them which is stored on your Blesta installation.
Simply go to Billing > Reports and select Json. Then select Client Data Portability.
We're using 384 for our example you can view it by going to the client's profile which looks something like:
The file you download will be what you pass to the client which looks something like this:
The MAIN information included in the file as-well as other things are as thus:
All this will be available unless you DELETE the account. To delete the account you will need to re-enter your password.