os 10.7.5 to os 10.10
I'm trying to get from os 10.7.5 to yosemite. I get an unknown error when i try to download from the app store. I tried a direct downoad of os10.10.4, but it says I need 10.10 first. I can't seem to find just os 10.10. Help.
MacBook Pro, Mac OS X (10.7.5)