keyboard – Mac key reallocation

I just bought a KeyChron K4 keyboard (Gateron Blue switches, it's excellent) and the design is a bit different from the 104 standard keys.

I want to exchange two keys: the problem is with Karbiner if I change a key to the other function (num / clear to a small key of the), when I try to change the key of the (original) to the new num / clear, it actually changes the key of the one I just created.

I looked at Ukulele (I actually installed it), but it seems too complicated. Is there an easy to understand tutorial for this?

Is the BetterTouch Tool easier to use and will do what you want? Thank you.