What's the difference between; I want it I want to have it
And what is the reason?
Thank you in advance
There isn't much difference, as far as I can tell. There might be more immediacy and emphasis to want than want to have. For example:
He wants sex.
He wants to have sex.
People might disagree, but I think he wants sex could connote a stronger or more spontaneous urge than he wants to have sex, which connotes a more deliberate or more formalized or less immediate action.
EDIT: Adding some more examples just so people can draw conclusions for themselves:
I want the kidney transplant.
I want to have the kidney transplant.
The CEO wanted the Ferrari.
The CEO wanted to have the Ferrari.
The dog wants a kiss.
The dog wants to have a kiss.
We wanted a World Series championship.
We wanted to have a World Series championship.
Looking at these examples, I still believe wants to have implies a more deliberate or more formalized action. The desire in wants is perhaps more ephemeral or spontaneous.
For example, it's a tiny bit awkward to say The dog wants to have a kiss because it implies that the dog is thinking about it and has made a conscious decision that he would like you to kiss him. We know dogs don't reason in this way, so it's a little humorous to say a dog wants to have a kiss. Instead, we would say, "The dog wants a kiss." It's a simple, spontaneous desire.