I have 3 Projekt i dont need. How can i quit this Projetzs? In have leave 3 Projekt in my boinc messenger but in http://www.boincstats.com is he always shown.

you will always have these credits whether you like it or not.

i have no credits at this projects that i want to leave.

I only see one project in your stats. Sztaki.

under the menu point BAM|Ressourcen and projektlist
i have 6 projekts 4 i want to leave.

They are just on your BAM list, you aren't really 'on' the projects. So you wouldn't be 'leaving' from them. You can't remove them from BAM list, and anyway it makes no difference to have them there or not.

yes but the overwiew is bethehr with 2 as with 6.
but i can nothing do.
thanks for help

No currently there is no way of deleting an account at the projects.
But you can do the following (NOTE: That these steps are very risky and are not tested!):
1. Delete your BAM! account
2. Change your email to some other email at the projects in which you don't want to participate.
3. Create a new BAM! account and when asked enter the "good" email, from the projects that you want to be listed.
4. Reattach your BOINC Manager to BAM!