New computer, and itunes wont let me install my apps

My Ipod touch 8g died so I sent it in for a replacement. I also sold my mac mini and bought a new macbook pro. after restoring my backup and trying to sync my ipod it says I cant sync my apps.

I went to itunes store and account info. It says I only have one computer authorized to use itunes. How do I remove my old computer and set it up for my new one? Do I need to call tech support?