You can update to whichever release your license entitles you. This is different for different licenses. The download center should have the accurate list of all the releases you are allowed to use. If it doesn't, you should use the telephone icon at the top of the page to contact Mathworks support directly.
In general free updates don't exist (to newer releases, bug fixes are free). They are either included as a service (in the SMS), or your company/university pays for it as part of a license agreement.