There are two ways to adjust the cord, either by using the speed cinch or the shirt clip.
The cinch helps to keep the cord off your neck and shoulders, which is especially useful for the over-ear fit. To adjust the cinch do the following:
Put the X4 earbuds in your ears.
Grab the cord beneath the cinch with one hand. With your other hand adjust the cinch up or down until you find the right cord length to get a snug fit with no excessive slack.