Well, hello all!
All this like tittle say
Here where I find it and gonna copy all of it here
http://www.geek.com/games/new-3ds-c-stick-can-be-replaced-with-a-psp-analog-stick-1648121/
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For the longest time gaming handhelds did not have a second analog stick, making certain games a pain to control (shooters) and 3D camera control impossible. Sony decided to fix this on the PS Vita by adding a second stick. Nintendo dragged its feet a lot longer, but eventually came up with the C-Stick, which is a nub, not a stick.

Not everyone likes the C-Stick on the New 3DS and New 3DS XL. It doesn’t allow for much movement, can become uncomfortable to use during extended play, and apparently oils can build up in it making it more difficult to use. However, there’s a surprising solution to the problem, and it comes in the form of the analog stick cap found on a PSP-1000.

The realization this works came via an experiment by Ryan Hirsch who detailed the installation on Reddit. The C-Stick nub just pops out using the tip of a screwdriver. Then the PSP analog stick cap can be placed over the hole and with a bit of pressure pops into place. It actually sits a little lower than the C-Stick nub, so causes no issues when the 3DS is closed.

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Obviously, there’s a risk you could damage your 3DS by attempting this, but it looks easy enough. If you’re not happy with the C-Stick then why not, right? Replacement PSP stick caps can be picked up for a couple of dollars, and I’ve seen replacement C-Stick caps for $10. So it’s not exactly an expensive experiment to conduct.

nick martin10:
BUT WAIT! Don't cut your old c-stick.....Its way too easy to just unscrew the back plate remove the screws securing the c-stick module and simply pop the rubbery thing off.. !!!