While it sounds like most are moving to iCloud pretty smoothly, it's always a good idea to create a backup of your data before things like this. Here's how to backup your contacts and calendars. Open Address Book, then choose File > Export > Address Book Archive. And then open iCal, then choose File > Export > iCal Archive. In both situations, just export to the desktop. Then, once you've confirmed that your migration went seamlessly, you can move them to the trash.
I am an Apple Certified Support Professional with over a decade of experience supporting families, schools, and businesses. Tech has always captured my imagination, but it's not my only passion. I'm an ordained Anglican minister; Aeropress is a daily ritual of mine; I've driven across Mongolia; and I'm the father of three girls. I hope to provide for you a balanced and realistic perspective into the practicality of technology.