How difficult is it to change brake and gear cables on a bike?

I got a new (second-hand) bike this week. It's got swept back handlebars and I just don't like them after riding with them for a few days. It feels like I'm holding onto a zimmer frame and I hate how I have to hold my arms to the sides

I wanna replace em with cool, non-lame handlebars like these

l will almost certainly need longer cables for my brakes and shifters though. How much of a pain in the ass would swapping out the cables be?