You can't, it's been asked many times on there forum for it to be changed or user customizable, but they won't or can't implement it.
One guy created a custom EPGselection.pyo file that did it, I myself use it, but it gets overwritten on each update and you have to put it back in.
This is weird because when i got my box, it came pre-installed with firmware and the Blue HD skin and it has + and - 24hrs on the EPG and the up down page buttons work fine but i've bought another box and put firmware and Blue HD skin on myself and in place of the + and - 24 hrs is IMDB and the page up / down doesn't work like it does on my original box with exactly the same skin but instead, as you've said above - it's buttons 2 and 8 ... confused :/
