You can simply add additional partitions by pressing the plus button and then using section control (2) to adjust its size. Press the Partition button on the top and a new window with a partitions allocation pie chart will appear.On the picture below you can see our test configuration - external USB drive with a single partition “Test-Resizing”.Open Disk Utility by typing the first part of its title in Spotlight search:.
So, let’s check how to shrink a partition using Disk Utility: You can shrink partition size with no data loss if there is unused space in its volume (remember, volume is a layer of file systems above a partition). It is a common partition table for the latest Macs, but check it anyway. You can avoid data loss while resizing the partition only for GUID-partitioned drives.
If there is something in between - you need to remove it.