user-defined numbering

[Emil Pavlov]

I am using the Koma book class and I want to change the numbering style 
of chapter, sections, etc. It is currently:

1 Chapter dfg
1.1 Section dhd
1.1.1 Subsection sfgh
1.1.2 Subsection dfds
1.1.2.1 Subsubsection fjkf
and I'd prefer it was:

I Chapter dfg
1 Section dhd
a) Subsection sfgh
b) Subsection dfds
i) Subsubsection fjkf

Is this possible?

Thank you!

Emil