How do I set my speakers out of phase?
I chose to do phases in sound and noise cancellation (wavelengths and
  frequencies)


And


  What's the easiest way to get my speakers to be out of phase? Is
  wiring involved as many others have said?


At 1 kHz, the wavelength of sound is 34.4 cm so you don't really need to do anything other than move your sensing microphone (for the noise cancelling experiment), 8.6 cm from the midpoint position towards one speaker. The closer speaker signal will now be phase-advanced by 90 degrees and the more distant speaker will have a signal that is phase-retarded by 90 degrees and, the net effect, is that the two signals become exactly out of phase.

But this is only at 1 kHz. Should you decide to inject your set-up with 2 kHz then, despite the offset of 8.6 cm, the two speaker signals will be in phase. At 2 kHz, the offset would need to be 4.3 cm. At 10 kHz, the offset would need to be 0.86 cm.

But air temperature has to be factored in also: -


At 0 degC, the wavelength of 1 kHz is 33.2 cm
At 20 degC, the wavelength of 1 kHz is 34.3 cm
At 40 degC, the wavelength of 1 kHz is 35.5 cm


So, for pure cancellation you need to consider air temperature. All of this is because the speed of sound changes with temperature.

Of course, if there are a lot of reflections in the room (where you make measurements) then this experiment will be hard to do effectively BUT, reversing the phase by swapping one of the speaker wires would also be equally ineffective. Please take into account what I'm saying or you will waste your time. It's not surprising that we, as humans make use of two ears.


  My only problem is that my speakers are currently in phase (as
  speakers normally are)


They are only exactly "in phase" when the gap between them (for the measurement microphone) is exactly half way.

Wavelength calculator.

Footnote - noise cancellation is such a tricky business because slight movements can upset things and you turn a cancelling signal at one exact point into a noise enhancer a few centimetres away.