how to change the default keymap

Hi Chaps,

I need to change the current default key map.

currently I have the following:

Up/Down keys -->Open Cannel list

</> -->Zap/Change the channels 1 step up/down

I need to change as follows:

OK button-->Bring up Channel List

Up/down-->Change channel (next/previous)

</> --> increase/crease volume

Thanks in advance