Murthy, I don't know if you can flip a threaded headset. You can however, often get an adjustable stem for it that allows you to set the rise/angle.
To the OP: if your headset looks like this - http://bit.ly/HEylME
- it's a threadless headset. If it's set up as it looks in the pic, it's not possible to raise the height easily. You can lower
it for a more aggressive posture by (a) moving the spacers from under
the stem to over
it, and/or (2) flipping the stem so that it's angled downward. But why do you want to raise the handlebar height? If it's because it feels too low and you'd like a more upright posture, the best way out is to install a stem riser (steerer extender) as I have done on my bike. They are available online for upwards of $25 from brands such as Satori or Delta. They are not available in India, to the best of my knowledge.