Krell KSA300S power conversion

I have a Krell Ksa 300s and i want to convert power from 110v to 220v. Can someone help me out,please.I appreciate your help.Thanks.
Most of Krell amps have voltage switches inside. There should be 2 or 3 of them, each having position 1 and 2.
Thank you ELBEROTH2. I believe only the latest unit has switches in side of it.