The DSi always reports that there is a new version available, but when you trigger the update it says the system is up to date.
You don't have to be scared about firmware-updates, because the only to ways the system ask you to update is:
1. When you enter the DSIWare shop
2. Trigger the update manually in the configuration > Update
You can decide your own to update or not and if the update is going to be launched it will notice you to accept the terms of the new patch.