Polycom VVX410 changing line names

Hi,

I work for a architect company where we each have a Polycom VVX410 on our desks. We all recieve the call from the main line and can transfer calls to one another. But we have to guess which line is each phone as we cant figure out how to change the names of each line. 

How do i do this?

Also, each phone has a number on one of the lines, ranging from 700-706. what do these mean and do?

Thanks,

Sam