When you are at a new speed limit simply pull and hold the autopilot stalk to quickly revert to the new speed limit.
Speed
Activate ludicrous and get Spaceballs animation
Tap the T logo, on the “About Your Tesla” screen tap and hold the options badge.
Quickly change autopilot speed
By giving your scrollwheel a quick “zipp” while on autopilot it will speed up/down with increments of 5.