Have 3ds brother gave me XL

Hello,

I already have an ambassador 3ds and my brother just gave me his ambassador XL. NICE I KNOW RIGHT!

So we both already have things bought from the e-shop.....

SO.... What I was wondering is how do I just swap the system information. I don't want to have them both with my name I find that pointless and we lose all the things he bought, I would rather just back up his stuff on the 3DS incase he ever wants to go back.

My girlfriend also has a 3ds with nothing bought from the eshop just has saved games so I was thinking of just doing lots of system transfers...

I don't know the right way to go about this... so anything would help.

Thank you,