Welcome to Android Central! Where was your calendar data stored before the update? Was it associated with your Google account, or the local Phone account? If they were on your Google-based calendar, then it should just sync back. Check Google Calendar on the web to see if your events are there--if so, then they'll sync automatically.
If they were all on the Phone account, then it's possible they were lost in the update (although they really shouldn't have been). This is the problem with using the Phone account--it doesn't get backed up anywhere automatically. You have to manually back it up or sync using a 3rd party program like Kies.
Open the Calendar app, and check its settings. Make sure you just didn't remember to select the proper calendars to sync and display.