I bought a secondhand macbook pro (early 2011). It was running Yosemite, but I wanted to do a fresh install, as initially I didn't have the password.
I created a 2nd partition and installed a clean Yosemite on to it. I then wished to use that partition, so I "erased" the original partition in Disk Utility, so that it would let me erase it. Once I did that, the "-" button was selectable, but it will not actually delete the original partition, or modify the 2nd one at all.
I believe part of this is due to the the fact that the startup disc partition is on bottom and not on top, therefore I wouldn't be able to drag the partition to expand it to the max capacity of my computer.
That's all i'm trying to do. I realize that what I did was actually the long way (and pointless) to the results i'm trying to get. But how can I do this? I'm not worried about losing any info, as to me this comp is brand new. However, I don't have a USB stick with more than 8g, so I can't create a bootable disc for Yosemite, and pretty much need to install from app store download.