Change button in text view

[Lala]

Hello I've installed rockbox on my second hand gigabeat and it works great!
I'm in the process of puting a text version of wikipedia on it.  
I've read as much as I could of the rockbox website but I still can't find how to change the buttons. I must have seen it somewhere.
Is it possible in the text viewer to change the function to quit the viewer and to assign it to the 'left' button instead of the 'A' or 'power'?
It would make browsing all the articles much quicker.
Thank you...!