Can someone show me the technic of downshifting in to accelerate?

If you're cruising in 5th and you want to downshift to accelerate quicker, it's simple. Push the clutch down, blip the throttle to raise the engine speed by about 1000-1500, put the shifter in the next lower gear, and let out the clutch. Then, just mash the gas and go. If you want to go down another gear, just do the same thing, or when you take it out of gear, say going 5th to 3rd, instead of revving it up 1500 rpm, rev it up 2500-3000rpm then go straight to 3rd and let the clutch out. It really takes no thinking, and can be done in about 2 tenths of a second if taking your time.

No, you won't overrev the engine, unless you drop it into first gear. Most cars will do 62mph in 2nd gear by design, thanks to Motor Trend.

If you're doing 50 MPH at 2300 RPMs to downshift you would

1.) depress clutch and shift into neutral

2.) Slow using brake pedal down to about 1500 RPMs

3.) Shift into next lowest gear as you go off brake and give it gas.

You will be in the next lowest gear at the higher RPMs, around the 2500 RPM range.

No it won't over rev at that speed. The engine speed will increase by no more than 1000rpm and 3300 is not over reving

Press clutch at the same time as adding power/gas to your yanks, while changing gear.

To do that kind of things, you need to know your tires, and gear ratios, if you are tech enough you can do some simulations with a virtual car performance simulator, thats the best way than trying with your real car and damage it!

Check the sim here http://www.nxgtrsim.com/

Well my step mom is a master at down shifting. In our benz we had a 6 speed automatic with tip tronic shifting. All she would do is let off the gas down shift and floor it, shifting up when necessary.