How can I change the AppleID for apps

Hello,

My brother bought this MacBook Air for me when it had OS X Yosemite running on it, and later he updated it to El Capitan. Then he gifted the laptop to me so I created a new user account and started using apps.

Now, whenever I try to update iMovie, iPhoto or any other app that my brother had downloaded, it asks me the password of his AppleID. If I inserted my AppleID and my password instead, it gives an error as:

These apps cannot be accepted by your Apple ID.

These apps were already assigned to another Apple ID, and they will be available in that Apple ID's Purchases list. If you don't have access to that Apple ID and want to receive future updates, you will need to purchase the applications.

My question is, what are the options I have? Do I have to remove these apps and purchase them again using my AppleID? Is there a way to change the AppleID that is assigned to a certain app? Any help is highly appreciated.

Thanks.