How to increase the Power (HP) of an engine to enhance its initial pickup and speed in workshop (without making major modifications in design)?

1)Reduce the weight of the car

2 upgrade the exaust

3) you can always tune the car, i would advise to not try and flash it yourself you should have an EXPERT do it because its going to arange the air fuel rasios

Is it a turbocharged engine? -Chiptuning ;)

Improve fuel system and air intake.

1. Reduce the weight of the car. One of the easiest things that you can do right now to increase the horsepower is to make your vehicle as light as possible, which allows your vehicle accelerate better
2. Upgrade to a free-flowing exhaust system. Upgrading to a high-performance exhaust system can increase your horsepower by a measure of five to 10 on some natural aspiration vehicles, while vehicles with an additional supercharger can pick up much more. 
3. Research turbocharge and supercharge options. Installing a supercharger in a large-block engine, or a turbocharger in a smaller-block, will basically involve completely rebuilding your engine and upgrading the stress-bearing components of the engine, which will cost several thousands of dollars. It's a huge project, but is the most effective way to increase the horsepower of your vehicle.