Updating iMovie in App Store

I am the second user of my macbook air (boss got a new pro). His apple id is needed to update imovie in the app store. I have signed in on the App Store but i am still prompted to use his apple id to install the update. I don't need iMovie but I am fearful that this could present problems in the future. Updates for ML and MS office were successfully installed earlier but I can't get around the iMovie update...Any help will be appreciated!