Blank Theme is not showing up!

Hello Sir,I hope you are all in good health.:)

I have installed the magento blank theme but it is not showing up.Somebody told me to change the name of current theme directory to something else and rename the blank theme directory to default but I am unable to find both directories(the current theme directory and blank theme directory).I am using magento 1.7.0.0 on wamp server.can you please tell me where to find these directories so that I rename them and blank theme shows up after that.thank you.

The rename method is not a good choice, you should choose the blank theme in back end then it should show up fine.