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Go to the Partition pane in Disk Utility, select the partition you want to get rid of, and hit the Delete button.
 
Go to the Partition pane in Disk Utility, select the partition you want to get rid of, and hit the Delete button.

When I do that the delete button isnt avaible for me to press it's their but it has that gray transparent look that doesnt let me click it.
 
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