Checking which firmware version or menu version of your 3DS has is as easy as ABC:

• Select the System Settings icon on the HOME Menu, and tap "Open."
• The system's menu version will be displayed on the bottom right of the upper screen.

Almost all new 3DS firmware claim to have system stability improvements and other adjustments. What that really means is that the 3DS new firmware will block flashcarts such as R4 3DS and R4i. If you would like to keep your R4 and / or R4i to be usable on your 3DS, the best option is to disable the 3DS wifi function.