How can I do Slow Motion with the Sony Nex-7

Hi, it has been a while since i have bought this camera and I still cant figure out how to do Slow Motion. I put my camera settings to AVCHD 60i 17M with the shutterspeed at 1/125. theoratically, it is supposed to shoot 60 fps but when i transfer my files to my computer and that I check the properties of the videos, it says that they are at 29 fps.

How can I keep my video at 60 fps?

Thank you