1) Visit a local Wateen franchise office/shop before the billing date and get your plan changes there. This obviously requires a personal visit and depending upon how far the office is it would take up some of your precious time as well.
2) Open selfcare.wateen.com which is Wateen's official customer care portal and login using the details provided to you by Wateen at the time of registration and you would see an option there which says "Change Package" click on that and follow through and change your plan to whatever suits you. Once you have done this you would recieve a confirmation call from Wateen customer care to confirm these changes and your plan would then be changed.
3) You can call Wateen broadband customer care over the phone and speak to customer support and get them to change your plan over the phone itself. They would ask a couple of security questions to make sure it is indeed you who is calling them and they woulc be able to change your internet package for you.
If you know of another way then please post it here so every one can benefit. I hope this helps Wateen customers who come looking for information on how to change Wateen package.