Delete hard drive partition

I previously created a second partition on my MacBook Pro hard drive. I now wish to delete that partition and restore the space to the boot partition. The instructions in Disk Utility are not clear to me on how to accomplish this. Under the Partition tab, if I select the partition that I wish to delete, it states that “This partition can’t be modified.” (it also states “To erase and partition the selected disk ... etc” ... not what I want.)

Can someone explain in simple language how to remove the second partition and revert back to my original single partition configuration?