Boot up your computer with using a linux live-cd/dvd manjaro fedora puppy or other technical distro to start up what will have gparted and or the kde partition manager on it that does do everything unmounted to that will allways enable all necessary things to replace or resize partitions , beware backup first always the distro in any way to be safe with the beginning to experiments. but there are several kind of tools and all open source is free , here you see a part of the kde partition manager and here is to see that will you rezise a partition that it just not must be mounted , thats the most important step to get a working menu by changing partitions that will forget. but it must first are recognized before to choose the right drive partition manager is also good usable for Microsoft or Beos and several other partition cluster arts of other unix systems.
the live dvd will work fully from out the memory of your system thats why it cost many more time for handlings. whats also be better to resize partitions is most time to delete an 3 partition system from the right the third partition (if its handling mounting active partitions to resize up to the right site its differs how to boot with a bootmanager was configured after resizing from the middle partition the find theright cluster out.resize from the left site can made bootproblems, if you not can handle

Hi Steve,

Disk Utility have limitations when you try to resize the below disk to overtake its above available free spaces. I recommend you download Stellar Partition Manager software and create a bootable Media with it. Here is the process of booting up the Mac with USB:

1) Create disk image of Macintosh HDD with the Partition Manager Mac utility.

2) Double-Click the Disk Image to mount on Disk UtilityAttach an external hard drive with minimum 8GB of free spaces.

3) Now with Disk Utility Now restart Mac and press Option key to bring forth the startup menu.

4) Select the USB media to boot into Mac. When your Mac starts with the Bootable USB, the Stellar Partition Manager loads itself and allows you to resize the Mac hard drives and partition as desired, with the help of available free spaces.

Of course, the resizing is easily done with the software but the above process isn't absolutely free. You have to register the tool in order to execute all the software operations.