Follow the instructions on the provided link to deactive your account (you can later reactivate it if you like); but first read the next sentences.
It is unfortunately impossible to delete (erase, destruct, kill, etc.) your AdWords account. This is even more unfortunate because for the rest of your life, you will be responsible for any content on the web pages associated with your AdWords account (i.e. the ones for which you once advertised). This means, even if you sell your domain and someone else puts completely different content on it, YOU will remain responsible for that content complying with Google’s AdWords terms of service.
Does this sound faulty, mistaken, ridiculous, despotic, illogical, etc.? You tell Google! But this is how the company works. So think twice before you use AdWords.
The best (‘least worst’) thing you should do is keep your AdWords-associated domains and not sell them. Any competitor or ill-minded person could put ‘illegal’ content on it, for which you will be held responsible. Probably you can’t do much about it and your AdWords account may become locked, until you resolve the problem.
URLS:
http://adwords.google.com
http://support.google.com/adwords/bin/answer.py?hl=en&answer=2424604&rd=1