You're heading into a pretty sharp turn, and you're in 3rd gear at 4500rpm. You're going to need to slow down for the turn, and you know you're going to need to be in 2nd gear when you exit the turn in order to have the right amount of power.
Get on the brakes, start slowing down
brakes still on, clutch in
shift to neutral, blip gas with the side of your right foot
shift to 2nd gear, clutch out
gas and accelerate as you exit the turn
When you blip the gas, you bring the engine's speed (rpm) up to the level that 2nd gear will be at when it engages. That way, the engine doesn't have to immediately speed up to that level when you let the clutch out. If it did, it could upset the balance of the car and send you sliding off the road. And that would be bad.