How to get phone back to stock?

[jmsmackdown]

So I installed CWM and am Using CM10 on my S2 Skyrocket and I am trading it to a buddy who just wants it plain factory stock with no CWM and no Custom Roms.

How do I get back to that point?

Also, after we trade do I have to go into an ATT store to get our services switched? Or do I call them?