how to update ios 5.0.1 to 6.1.2?? pls help!!!

Take a look at this link, http://support.apple.com/kb/HT4623

You can't update to iOS 6.1.2, only 6.1.3

If you are alread on iOS 5+ then you should have a Settings > General > Software Update option for direct update on your iPad, or you can do it by connecting the iPad to your computer's iTunes and clicking the Check For Updates button on the iPad device's Summary tab

Correct, only the current version is 'signed' by Apple, so you can only update to that