Some of the previous answers were based on earlier injectors.
1) Pull the red slide lock (if still there) up towards the hood. It might break off. Thats ok.. its not really needed.
2) You could push on the button, but with the age it is better to use a small pick. At the very bottom of the plug use a small pick to gently pull the clip up a bit.. like 1/16". While doing that pull the plug away from the injector.