Unable to change volume size on WD My Passport Wireless I have been trying to partion my WD My Passport External harddrive that has already got data on it. All of the guides I see on the internet tell you to resize the current volume to do so. I don't have the tab to do this in disk utilities.
Using the Disk Utility you should see something like this



Select the external disk (called Hitachi in this example)

Click on the partition you want to work on, and resize it