There is no A-B line management in a 500. You can create and select, but you can't delete or rename. Real poor in my opinion.
I understand the 750 is no better in this department.
Farm Works talks about being able to manage lines with their high $$ program but I've never seen any details on how well it works or how painful it is to get the software to do it.
FMX is supposed to be able to manage A-B lines very nicely. After having set up and used Farm Works, I'd much rather spend a few bucks more and get an FMX.