Pull the red lock out by prying it out with a jeweler's screwdriver, then use that screwdriver to release the plastic locking tangs which hold the terminals in. You have to push the locking tangs away from the terminal at the same time as you pull it out the back. It may help to have someone else pull as you push. You can pull the terminals out the back, right through the rubber wire seal. EDIT: You may find it easier to use a dental pick to release the locking tangs, but I've always used a jeweler's screwdriver.
That connector dates back to at least the late 80s, by the way. Pretty sure it was first used as a MAF sensor connector.