I cannot install SP3 as I need to install SP2 first, but I cannot install SP2 as I get the following error message running the latest version of Yosemite: 

"This version for AutoCAD 2013 for Mac requres OS X 10.6.4 or later".

I also cannot use the Remove AutoCAD 2013 app because it does not run correctly on Yosemite, so I can't reinstall AutoCAD 2013 either.