How to install shift cables for a 1980 70hp Evinrude?

-I am a big newbie at these things, but I am going to my local boat shop and buying new shifter cables.

Can someone please explain to me how to do this? I took a look at my control box and I believe there were two shifter cables? It is a 15.5 foot boat, so would I need an 18ft cable?



Any help would be appreciated.



Thanks