why wont my app store let me update applications?

Every time I try to update things like pages, keynote, etc. the app store pops up the little box that says "This update is not available for this Apple ID either because it was bought by a different user or the item was refunded or cancelled." How do I fix this? I bought my Mac second hand with these applications already installed, I don't have access to the original Apple ID that was used to install the applications.