You cannot use the notebook on your lap or a sofa -- you're blocking the air intake for the cooling system.  The notebook needs to used on a hard, flat surface.

If the system continues to heat, reduce the load on the system or change the power plan to something that runs cooler.  The worst thing you can do is set the system for maximum performance, which will lead to it heating up and throttling.

Even I am keeping the laptop on flat face, still am feeling heat on keyboard

See the second part of the reply -- reduce the load on the system and change the power management settings until the heat issue is reduced.  You can't eliminate heat entirely -- and this system has some power-intensive hardware in a slim design, meaning you have to work within the thermal parameters of its design.  The other possibility is an external cooling pad, which can also help.

Power management I changed to ultra performance. Still same problem (I cannot touch top left part of keyboard)                                                                                                                                                       Actually, I have 8GB ram Dell inspiron it's working fine from last 4 years, I thought to upgrade 16 GB ram  So I purchased new in last October 23.                                                                                                        Load on the ram only 70 to 80 %, for this it is generating heat.

Ultra performance will worsen the heat problem -- it needs to be set for balanced performance.

The largest source of heat in the system is the GPU.  Set the system to use the integrated GPU for all applications that don't need the discrete one.  That will reduce the heat problem.

Problems: 

1) Screen is also heating

2) Left top keyboard heating, cannot touch keyboard

3) It's just 6 months back I had purchased

1.  Heat rises;  if the system is overheating, the screen will be affected.

2.  That's likely where the CPU and or GPU chips are located.

3.  If so, and you've tried changing the power management and reducing the number of programs running, call Dell for warranty service.

Am just watching YouTube & no other programs are running.