Sorry, there is absolutely no way to do blurring in paint.
In fact, there is absolutely no way of doing anything with paint except filling images with white blocks and trying to copy its functionality for code developer amateurs.
But really, to support your issue: You could get paint.net.
It's entirely donationware, which means that you
can donate money to the developers, but you need not. When interested, download at
http://www.getpaint.net/ and ask here again, then I can help you with the blurring process.
greetings, s.