Radio split screen
 

Hey guys,
I'm looking to pick up an 06' X5 with nav and I'm already trying to figure out my first mod. I'm wanting to do the radio split screen so I got a copy of V26 and V31. So would I just upgrade to V31 and then down to V26 and then back to V31? Or do I need to go to a lower software version when downgrading? I have a copy of V21.1 as well. I'm not sure what version is on it currently since I'm picking it up on Saturday. Any help is appreciated. Thanks.