USB Drive issues

I have a usb drive that I used on a Mac that I have two partitions on. The first partition I used for backups and the second I used for everything else. It is formatted fat32. I plug it into my raspberry pi running Raspbian and I can open the files but I can not copy from one to the other or resize using Gparted. Can someone point me in the right direction to fix this. I would like to keep the backups in case I get another Mac and have access to the other drive for history. I also would like to add a partition for the raspberry pi.