Remove Access Rights

Hello,
I have a little problem. I wrote an application, which I'm using for enable access into the registers for specified user.
For example: I have a key HKLM\Software\TestKey and I need programmatically add the user name FRIEND into the access list for this key with READ_ACCESS.
Well, everything is OK, the application works right. But I need too remove the rights too. In this case I have a problem. I don't know a way, how to remove rights for specified user (or remove user).
Is anybody know, how to is a possible to make it?
I'm on 'the end' of my experiences ...
Thanx for all helps & hints

Best regards
Petr Havlicek
[email protected]