N14 is 7 protons + 7 neutrons. Add a neutron to that and you've got N15 (7 protons + 8 neutrons).
To get to C14 from N14 you've got to turn a proton to a neutron. (Carbon has 6 protons. C13 has 6 protons and 7 neutrons, C14 has 6 protons and 8 neutrons).
Roughly speaking proton + electron <-> neutron, so
N14 + beta <-> C14
Obviously you could get from C13 to C14 by neutron capture, but that's not what we're talking about here.
or am I dumb?