how do I update my original iPad to newest version?

Easy. Go to the Apple store and buy an iPad 3. 😉

Its too easy.

connect ur iPad to a mac or a pc and open itunes

from the left panel select ur iPad

click the update or check for update button and follow the instructions

if no update is available then press restore and follow the instructions

See iOS: How to update your iPhone, iPad, or iPod touch

http://support.apple.com/kb/HT4623

If you are currently running an iOS lower than 5.0, click on the "Update your device using iTunes".

 Cheers, Tom 😉