How can I go back to ICS after JB OTA updates? My phone is HTC One S VelliC2 and received the JB OTA updates.

However, I could not get used to it. So how can I return to ICS? Can I use the HTC Android 4.03 RUU file? Now the Hboot version has updates to 3.1 and it was 2.09 before the OTA updates. Does the Hboot version matters?

Thanks in advance.
If you can find an original stock ROM for your device (I assume your device is not rooted etc.), or any fitting custom ROM (in case it is rooted etc.), you could factory-reset your device and then flash that ROM. See Where can I find stock or custom ROMs for my Android device? for available ROM sources.