Is it possible to delete my both accounts (Blacky and Blacky27).
If it is possible please delete

Blacky27

You should be able to do it yourself, others have done it successfully. A cautionary word, though; if you are deleting your account in an attempt to fix a credit/CPID/stats issue, you may actually make the problem worse. That is, unfortunately, how I know people have been able to delete their accounts themselves.

No, it's not possible to delete your BAM! account.

Why not? I'm pretty sure that there are a lot of people who stop running BOINC at some time, and don't wish to have their e-mail addresses and other personal information retained in your database forever. And I'm guessing that there is some overhead cost to you associated with maintaining an ever growing database as well?

There is only 1 method to unpersonalize your information in BOINC-world:

Detach all your computers from all projects.
Delete hosts on the projects (only possible if no tasks visible anymore)
Give a new username to all the project accounts together with a new (fake) e-mail address, a new password and forget all for ever.

Detaching all your Computers from all projects is practically impossible to do with all the projects that have shut down already unless BAM does it for you. Your Computer info is stored at the Closed Projects too and if the Projects are offline I don't see how BAM or you could do that.

The best way is like you say though to change your e-mail address & user name here at BOINCstats/BAM so you would have just a dummy account ...