Major releases
NetSuite has two major releases per year. The precise schedule changes each year but you can expect the first release in or around April and the second in August, give or take. The releases are usually designated the format of release year.1 and release year.2.
It would be pretty difficult to upgrade each and every NetSuite database on the same day, not to mention risky, so NetSuite phases a release over a period of a few weeks. This enables them to upgrade customers over that period of time. Think of it as NetSuite upgrading 20 percent of customer databases every weekend for 5 weeks. The actual schedule differs each year.
What release am I on?
The easiest way to tell the precise release that you are working on is to check out the bottom of the home dashboard:

This database is on the 2018.2 release
Notifications
You must be thinking: how will I be notified of a new release?
NetSuite will send the primary contact notifications of upcoming releases. In addition, the administrator can...