iBooks has become the default application to open .pdfs. How can I change this?

Thank you. I've tried the {command info} option on files with .pdf and hit change all to open in preview. I'm not comfortable doing the other recommended steps in the article myself. I don't want to mess up the computer when I'm not confident enough in my computer skills!! Thank you for your quick reply!

Correct. When I tried the first time I couldn't. When I went back to try again I hit the default option that was displayed and then it allowed me to hit "change all". When I do school with my kids each day (online school) I have to open their downloads with the "open with" option. I always select Preview and check the box to apply to "all documents like this one." Then, when I go to a different kids class and have to download a worksheet it opens up in ibooks again.

I'm hoping that there is something different about changing it in the "info" mode so that they all open that way. I'll find out tomorrow when we start school again!