There is an upgrade feature now standard in e-smith 4.1 (it was there in 4.0 but undocumented).
When you are about to install 4.1, there is an option screen to do one of three things:
1. install
2. install with software RAID support
3. upgrade
Make sure you still do a backup before you do the upgrade, just standard procedure for safety sake, and then let the upgrade do its work for you.
Bear in mind, the upgrade takes a little longer than the installation as its doing much more work.
Enjoy.
Jason