shaivalinikashyap,
As long as they are getting smaller in size, you probably do not too much to worry about.
Lumps and bumps about the head are extremely common. There are many skin conditions which can cause lumps, such as sebaceous or dermoid cysts.
It is also common for benign extostosis to occur on the skull. They are basically bone spurs, which are sessile (for sort of mounds, rather than sharp spurs). But, since your lumps are getting smaller, they are not this condition.
Also, maligant tumors are actually quite rare. And, they do not get smaller in size.
Again, you probably do not have a lot to worry about. But, if you are really concerned about them, have your physician take a look at them.
Good luck.