What test should I take to get my CDL class A license?

What test should I take to get my CDL class A license?? I want to get my CDL Class A license permit I just want to drive the regular 18 wheelers what part of the exam should I study? And what test should I ask for when I go to the DMV to get my permit.. And I already have a CDL Class B license with passenger and airbreaks for 9 years already and want to upgrade to CDL class A driving the regular 18 wheelers thanks..