Difficulty level Whats your opinion

Yes it will be difficult. As both are 2 different platforms with their own limitations

Secondly if you experienced in Web I would suggest continue in that.

Sir,

But situations may arise due to some reasons asked to work on windows and shift from web-windows. Then what would be the best decision?

Well its depends on person to person and situation to situation. If you are offered high prestige job and salary then you can think on it.

If your experience in ASP.Net is 2+ its not good to decision to change

Sir,

I have just 1 yr exp in asp.net but asked to work on windows application. What is your opinion on this? As i cant quit the job atleast for 4 months

You need to decide that. Also it depends on your likes and dislikes