You can use Speed Mind Maths to practice these techniques, and you will see how you can do mental math more quickly every day. It's just a matter of repeating the mathematical operations over and over again. If you haven't mastered calculations with small figures, it will be particularly hard to master adding, subtracting, multiplying and dividing large numbers. So, you will start to practice with small figures until you can do math up to 2000% more quickly.
Speed Mind Maths' interface is nothing spectacular; in fact, it's quite simple, but it does its job perfectly. You can decide if the operations will appear horizontally or vertically, select addition, subtraction, multiplication or division, choose the number of figures and the method used to solve the calculation...
If you want to be able to do math calculations more quickly, Speed Mind Maths is a program that is similar to the famous Brain Training. It will help you a lot, but remember, you have to practice consistently in order to note the improvement.