The Yosemite partition is 75gb of the 256gb ssd. I seem to remember when installing Yosemite there was one issue or users choice re the iCloud services. We could have it on either of Mavericks or Yosemite but not both. Am I remembering that correctly or am I screwed up? Most of all the data that I want to keep could be found on iCloud. So maybe I ma worried about a non issue.
Thanks
Paky
Backup first before you do this in case things go badly.
Okay... so all the data you want to keep is in Yosemite yes?
I am also assuming Yosemite is on the second (lower) partition if you look in Disk Utility.
When Yosemite is installed on a second partition, for some reason it turns that partition into a core storage volume. You will need to turn that off to do this.
So do a command-option-r (hold all three keys at once) boot to Internet recovery. You will need to select your wifi then you will see a spinning globe while the recovery utility downloads and starts. Once that happens you will see the recovery screen.
Go to the Utilities menu and start Terminal then enter the command below. You should get a message the the conversion worked. Then quit Terminal.
Now start Disk Utility and go to the restore tab. Drag the Yosemite partition into the source tab and drag the Mavericks partition into the destination tab and click restore. That will clone the Yosemite volume over top of the Mavericks volume wiping any data in the Mavericks volume.
Now reboot and hold the option key as it boots and pick the new Yosemite volume to boot from.
Once you are booted to Yosemite on the old Mavericks partition, start Disk Utility and remove the old Yosemite volume from the bottom then expand the top (now Yosemite) partition on top down to fill the empty space and apply the change. Give
this a look.
Now open System Prefs and in the Startup Disk pane set the Yosemite partition as the boot disk, then restart.
That should do it.