Remapping Options:

Step by step Remapping Tutorial for N00bs: CLICK HERE

Need to know more about registry configurations and detailed information about what every byte mean then Option B tutorial is for you. But if you just want to remap your remote buttons quickly and easily then go for Option A.

Otherwise read this Wiki that has everything we ever know about MCE remotes Registry configuration data.

Option A:
Thanks to Oskar aka oskii For creating this Fantastic little app that'll let you change your remote settings effortlessly, it can also read your setup so changing buttons has never been easier.
Visit Google Code host here
Download app from here

Note: MCERemoteMapper is designed for Windows and  requires ".NET Framework 2.0 or later" to be installed, if you do not have it see 'Direct Hot Links' for ".Net Framework" Latest release.

Option B:
Tutorial on How to change your Registry Settings:
For a more know how approach Download PDF Tutorial from here

A snapshot of the tutorial below.