How do you delete cue points

Well, there's a few differences between a main cue, hot cue, and memory cue point... so which is it you are referring to, and are you using software or is this just on a CDJ?

Thanks. I'm referring to the main cue of a track on the CDJ 

If you press the play/pause button (to stop playback, but not be "cued"), you can press the CUE button anytime to create a new main CUE point. If you have the CDJ set to load the track to the first memory / hot cue point, it will automatically set the main cue there. Check the UTILITY menu to see what your preference is, as you can also have it set to cue to the first portion of audio above a threshold dB level.

"you can press the CUE button anytime to create a new main CUE point"  once you do this, how do you undo it? 

You don't "undo" it, but you can set a main cue point anywhere you want by going to the "pause" mode and pressing the CUE button again.