The DS1052E has a 50Mhz maximum frequency, but it has exactly the same hardware (as far as the reverse-engineering folks can tell) as the DS1102E, which has a 100Mhz maximum. This guide will show you how to make the switch very easily using Linux. You can do it in Windows too, but it's a bit more involved, and Linux makes it really really easy.
I've attached the Rigol user guide for both units, in case you don't have one.
WARNING: It's entirely likely that this completely voids your warranty. Make sure you know what you're doing - you can brick your scope if you screw anything up.